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 $55.77   12.210%   $62.5795   $62.58   $62.60   $62.60  
  Purchase #2 $140.98   12.763%   $158.9733   $158.97   $158.95   $159.00  
  Purchase #3 $248.36   11.700%   $277.4181   $277.42   $277.40   $277.40  
  Purchase #4 $168.53   6.428%   $179.3631   $179.36   $179.35   $179.40  
  Purchase #5 $36.78   12.554%   $41.3974   $41.40   $41.40   $41.40  
  Purchase #6 $246.98   12.612%   $278.1291   $278.13   $278.15   $278.10  
  Purchase #7 $65.91   6.762%   $70.3668   $70.37   $70.35   $70.40  
  7 purchase totals = $963.31       $1,068.2273   $1,068.23   $1,068.20   $1,068.30