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 $142.56   5.761%   $150.7729   $150.77   $150.75   $150.80  
  Purchase #2 $205.73   11.189%   $228.7491   $228.75   $228.75   $228.70  
  Purchase #3 $120.87   13.137%   $136.7487   $136.75   $136.75   $136.70  
  Purchase #4 $174.46   7.124%   $186.8885   $186.89   $186.90   $186.90  
  Purchase #5 $129.43   9.176%   $141.3065   $141.31   $141.30   $141.30  
  Purchase #6 $161.60   12.105%   $181.1617   $181.16   $181.15   $181.20  
  Purchase #7 $33.63   4.672%   $35.2012   $35.20   $35.20   $35.20  
  7 purchase totals = $968.28       $1,060.8286   $1,060.83   $1,060.80   $1,060.80