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 $246.86   8.682%   $268.2924   $268.29   $268.30   $268.30  
  Purchase #2 $95.55   9.404%   $104.5355   $104.54   $104.55   $104.50  
  Purchase #3 $212.57   7.804%   $229.159   $229.16   $229.15   $229.20  
  Purchase #4 $240.93   4.399%   $251.5285   $251.53   $251.55   $251.50  
  Purchase #5 $147.38   8.116%   $159.3414   $159.34   $159.35   $159.30  
  Purchase #6 $209.62   10.870%   $232.4057   $232.41   $232.40   $232.40  
  Purchase #7 $141.35   12.169%   $158.5509   $158.55   $158.55   $158.60  
  7 purchase totals = $1,294.26       $1,403.8134   $1,403.82   $1,403.85   $1,403.80