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 $58.26   3.572%   $60.341   $60.34   $60.35   $60.30  
  Purchase #2 $149.42   6.299%   $158.832   $158.83   $158.85   $158.80  
  Purchase #3 $67.62   9.838%   $74.2725   $74.27   $74.25   $74.30  
  Purchase #4 $236.78   8.650%   $257.2615   $257.26   $257.25   $257.30  
  Purchase #5 $96.51   5.198%   $101.5266   $101.53   $101.55   $101.50  
  Purchase #6 $55.98   6.830%   $59.8034   $59.80   $59.80   $59.80  
  Purchase #7 $112.73   3.512%   $116.6891   $116.69   $116.70   $116.70  
  7 purchase totals = $777.30       $828.7261   $828.72   $828.75   $828.70