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 $59.66   8.338%   $64.6345   $64.63   $64.65   $64.60  
  Purchase #2 $28.75   11.829%   $32.1508   $32.15   $32.15   $32.20  
  Purchase #3 $153.54   9.583%   $168.2537   $168.25   $168.25   $168.30  
  Purchase #4 $189.39   6.823%   $202.3121   $202.31   $202.30   $202.30  
  Purchase #5 $45.54   5.172%   $47.8953   $47.90   $47.90   $47.90  
  Purchase #6 $95.29   9.424%   $104.2701   $104.27   $104.25   $104.30  
  Purchase #7 $206.43   4.138%   $214.9721   $214.97   $214.95   $215.00  
  7 purchase totals = $778.60       $834.4886   $834.48   $834.45   $834.60