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 $63.45   6.767%   $67.7437   $67.74   $67.75   $67.70  
  Purchase #2 $195.80   10.826%   $216.9973   $217.00   $217.00   $217.00  
  Purchase #3 $159.38   11.193%   $177.2194   $177.22   $177.20   $177.20  
  Purchase #4 $111.95   12.422%   $125.8564   $125.86   $125.85   $125.90  
  Purchase #5 $132.27   5.644%   $139.7353   $139.74   $139.75   $139.70  
  Purchase #6 $36.62   10.263%   $40.3783   $40.38   $40.40   $40.40  
  Purchase #7 $91.73   4.177%   $95.5616   $95.56   $95.55   $95.60  
  7 purchase totals = $791.20       $863.4920   $863.50   $863.50   $863.50