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 $84.42   11.736%   $94.3275   $94.33   $94.35   $94.30  
  Purchase #2 $125.63   3.828%   $130.4391   $130.44   $130.45   $130.40  
  Purchase #3 $243.94   8.229%   $264.0138   $264.01   $264.00   $264.00  
  Purchase #4 $23.67   6.837%   $25.2883   $25.29   $25.30   $25.30  
  Purchase #5 $88.49   11.142%   $98.3496   $98.35   $98.35   $98.30  
  Purchase #6 $143.97   11.510%   $160.5409   $160.54   $160.55   $160.50  
  Purchase #7 $56.74   13.739%   $64.5355   $64.54   $64.55   $64.50  
  7 purchase totals = $766.86       $837.4947   $837.50   $837.55   $837.30