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 $126.55   11.434%   $141.0197   $141.02   $141.00   $141.00  
  Purchase #2 $49.74   3.654%   $51.5575   $51.56   $51.55   $51.60  
  Purchase #3 $244.69   8.715%   $266.0147   $266.01   $266.00   $266.00  
  Purchase #4 $56.95   6.340%   $60.5606   $60.56   $60.55   $60.60  
  Purchase #5 $97.38   6.726%   $103.9298   $103.93   $103.95   $103.90  
  Purchase #6 $185.25   13.540%   $210.3329   $210.33   $210.35   $210.30  
  Purchase #7 $177.53   10.302%   $195.8191   $195.82   $195.80   $195.80  
  7 purchase totals = $938.09       $1,029.2343   $1,029.23   $1,029.20   $1,029.20