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 $90.71   6.580%   $96.6787   $96.68   $96.70   $96.70  
  Purchase #2 $146.80   10.606%   $162.3696   $162.37   $162.35   $162.40  
  Purchase #3 $187.46   3.865%   $194.7053   $194.71   $194.70   $194.70  
  Purchase #4 $32.61   9.592%   $35.738   $35.74   $35.75   $35.70  
  Purchase #5 $68.54   5.436%   $72.2658   $72.27   $72.25   $72.30  
  Purchase #6 $7.45   10.507%   $8.2328   $8.23   $8.25   $8.20  
  Purchase #7 $129.48   8.756%   $140.8173   $140.82   $140.80   $140.80  
  7 purchase totals = $663.05       $710.8075   $710.82   $710.80   $710.80