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 $244.71   5.155%   $257.3248   $257.32   $257.30   $257.30  
  Purchase #2 $90.85   7.354%   $97.5311   $97.53   $97.55   $97.50  
  Purchase #3 $70.91   4.172%   $73.8684   $73.87   $73.85   $73.90  
  Purchase #4 $178.55   4.842%   $187.1954   $187.20   $187.20   $187.20  
  Purchase #5 $249.72   7.185%   $267.6624   $267.66   $267.65   $267.70  
  Purchase #6 $36.91   12.428%   $41.4972   $41.50   $41.50   $41.50  
  Purchase #7 $35.58   13.535%   $40.3958   $40.40   $40.40   $40.40  
  7 purchase totals = $907.23       $965.4751   $965.48   $965.45   $965.50