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 $48.97   12.686%   $55.1823   $55.18   $55.20   $55.20  
  Purchase #2 $20.72   8.354%   $22.4509   $22.45   $22.45   $22.50  
  Purchase #3 $170.56   4.736%   $178.6377   $178.64   $178.65   $178.60  
  Purchase #4 $235.87   5.263%   $248.2838   $248.28   $248.30   $248.30  
  Purchase #5 $62.76   7.755%   $67.627   $67.63   $67.65   $67.60  
  Purchase #6 $237.56   9.769%   $260.7672   $260.77   $260.75   $260.80  
  Purchase #7 $52.46   12.674%   $59.1088   $59.11   $59.10   $59.10  
  7 purchase totals = $828.90       $892.0577   $892.06   $892.10   $892.10