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 $83.82   12.626%   $94.4031   $94.40   $94.40   $94.40  
  Purchase #2 $211.58   9.479%   $231.6357   $231.64   $231.65   $231.60  
  Purchase #3 $104.34   12.497%   $117.3794   $117.38   $117.40   $117.40  
  Purchase #4 $93.54   13.742%   $106.3943   $106.39   $106.40   $106.40  
  Purchase #5 $220.98   6.854%   $236.126   $236.13   $236.15   $236.10  
  Purchase #6 $7.48   13.738%   $8.5076   $8.51   $8.50   $8.50  
  Purchase #7 $26.87   13.666%   $30.5421   $30.54   $30.55   $30.50  
  7 purchase totals = $748.61       $824.9882   $824.99   $825.05   $824.90