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 $232.32   5.147%   $244.2775   $244.28   $244.30   $244.30  
  Purchase #2 $214.62   3.231%   $221.5544   $221.55   $221.55   $221.60  
  Purchase #3 $127.26   5.839%   $134.6907   $134.69   $134.70   $134.70  
  Purchase #4 $50.45   12.705%   $56.8597   $56.86   $56.85   $56.90  
  Purchase #5 $113.45   9.719%   $124.4762   $124.48   $124.50   $124.50  
  Purchase #6 $166.59   7.256%   $178.6778   $178.68   $178.70   $178.70  
  Purchase #7 $61.57   5.679%   $65.0666   $65.07   $65.05   $65.10  
  7 purchase totals = $966.26       $1,025.6029   $1,025.61   $1,025.65   $1,025.80