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 $176.85   13.785%   $201.2288   $201.23   $201.25   $201.20  
  Purchase #2 $94.89   7.792%   $102.2838   $102.28   $102.30   $102.30  
  Purchase #3 $136.95   11.130%   $152.1925   $152.19   $152.20   $152.20  
  Purchase #4 $236.86   11.578%   $264.2837   $264.28   $264.30   $264.30  
  Purchase #5 $29.97   11.690%   $33.4735   $33.47   $33.45   $33.50  
  Purchase #6 $234.89   3.237%   $242.4934   $242.49   $242.50   $242.50  
  Purchase #7 $209.99   5.635%   $221.8229   $221.82   $221.80   $221.80  
  7 purchase totals = $1,120.40       $1,217.7786   $1,217.76   $1,217.80   $1,217.80