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 $63.49   10.725%   $70.2993   $70.30   $70.30   $70.30  
  Purchase #2 $59.47   11.470%   $66.2912   $66.29   $66.30   $66.30  
  Purchase #3 $30.89   3.452%   $31.9563   $31.96   $31.95   $32.00  
  Purchase #4 $87.32   5.261%   $91.9139   $91.91   $91.90   $91.90  
  Purchase #5 $51.66   4.863%   $54.1722   $54.17   $54.15   $54.20  
  Purchase #6 $243.46   11.697%   $271.9375   $271.94   $271.95   $271.90  
  Purchase #7 $216.71   10.847%   $240.2165   $240.22   $240.20   $240.20  
  7 purchase totals = $753.00       $826.7869   $826.79   $826.75   $826.80