Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.89   8.543%   $106.2527   $106.25   $106.25   $106.30  
  Purchase #2 $150.50   7.869%   $162.3428   $162.34   $162.35   $162.30  
  Purchase #3 $65.62   7.559%   $70.5802   $70.58   $70.60   $70.60  
  Purchase #4 $96.80   11.376%   $107.812   $107.81   $107.80   $107.80  
  Purchase #5 $161.34   12.331%   $181.2348   $181.23   $181.25   $181.20  
  Purchase #6 $141.88   10.449%   $156.705   $156.71   $156.70   $156.70  
  Purchase #7 $242.55   10.279%   $267.4817   $267.48   $267.50   $267.50  
  7 purchase totals = $956.58       $1,052.4092   $1,052.40   $1,052.45   $1,052.40