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 $212.98   13.370%   $241.4554   $241.46   $241.45   $241.50  
  Purchase #2 $99.96   3.133%   $103.0917   $103.09   $103.10   $103.10  
  Purchase #3 $21.76   10.406%   $24.0243   $24.02   $24.00   $24.00  
  Purchase #4 $112.87   5.274%   $118.8228   $118.82   $118.80   $118.80  
  Purchase #5 $47.28   3.525%   $48.9466   $48.95   $48.95   $48.90  
  Purchase #6 $159.77   10.245%   $176.1384   $176.14   $176.15   $176.10  
  Purchase #7 $213.90   13.143%   $242.0129   $242.01   $242.00   $242.00  
  7 purchase totals = $868.52       $954.4921   $954.49   $954.45   $954.40