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 $10.49   3.840%   $10.8928   $10.89   $10.90   $10.90  
  Purchase #2 $78.47   8.618%   $85.2325   $85.23   $85.25   $85.20  
  Purchase #3 $80.91   8.662%   $87.9184   $87.92   $87.90   $87.90  
  Purchase #4 $84.56   10.826%   $93.7145   $93.71   $93.70   $93.70  
  Purchase #5 $20.35   13.613%   $23.1202   $23.12   $23.10   $23.10  
  Purchase #6 $110.34   13.429%   $125.1576   $125.16   $125.15   $125.20  
  Purchase #7 $227.25   10.610%   $251.3612   $251.36   $251.35   $251.40  
  7 purchase totals = $612.37       $677.3972   $677.39   $677.35   $677.40