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 $59.90   4.196%   $62.4134   $62.41   $62.40   $62.40  
  Purchase #2 $246.62   13.418%   $279.7115   $279.71   $279.70   $279.70  
  Purchase #3 $181.96   6.807%   $194.346   $194.35   $194.35   $194.30  
  Purchase #4 $97.90   13.176%   $110.7993   $110.80   $110.80   $110.80  
  Purchase #5 $85.46   13.866%   $97.3099   $97.31   $97.30   $97.30  
  Purchase #6 $46.40   13.395%   $52.6153   $52.62   $52.60   $52.60  
  Purchase #7 $241.90   3.165%   $249.5561   $249.56   $249.55   $249.60  
  7 purchase totals = $960.14       $1,046.7515   $1,046.76   $1,046.70   $1,046.70