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 $226.78   12.697%   $255.5743   $255.57   $255.55   $255.60  
  Purchase #2 $49.99   9.788%   $54.883   $54.88   $54.90   $54.90  
  Purchase #3 $95.91   6.527%   $102.17   $102.17   $102.15   $102.20  
  Purchase #4 $248.80   12.416%   $279.691   $279.69   $279.70   $279.70  
  Purchase #5 $47.57   4.295%   $49.6131   $49.61   $49.60   $49.60  
  Purchase #6 $28.59   5.388%   $30.1304   $30.13   $30.15   $30.10  
  Purchase #7 $59.59   5.610%   $62.933   $62.93   $62.95   $62.90  
  7 purchase totals = $757.23       $834.9948   $834.98   $835.00   $835.00