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 $189.68   7.626%   $204.145   $204.15   $204.15   $204.10  
  Purchase #2 $166.35   9.711%   $182.5042   $182.50   $182.50   $182.50  
  Purchase #3 $24.44   6.823%   $26.1075   $26.11   $26.10   $26.10  
  Purchase #4 $61.32   13.532%   $69.6178   $69.62   $69.60   $69.60  
  Purchase #5 $158.29   12.272%   $177.7153   $177.72   $177.70   $177.70  
  Purchase #6 $8.72   8.505%   $9.4616   $9.46   $9.45   $9.50  
  Purchase #7 $123.92   3.751%   $128.5682   $128.57   $128.55   $128.60  
  7 purchase totals = $732.72       $798.1196   $798.13   $798.05   $798.10