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 $24.76   7.462%   $26.6076   $26.61   $26.60   $26.60  
  Purchase #2 $37.69   6.738%   $40.2296   $40.23   $40.25   $40.20  
  Purchase #3 $120.75   4.528%   $126.2176   $126.22   $126.20   $126.20  
  Purchase #4 $61.40   7.597%   $66.0646   $66.06   $66.05   $66.10  
  Purchase #5 $16.40   7.811%   $17.681   $17.68   $17.70   $17.70  
  Purchase #6 $61.85   3.672%   $64.1211   $64.12   $64.10   $64.10  
  Purchase #7 $244.49   7.207%   $262.1104   $262.11   $262.10   $262.10  
  7 purchase totals = $567.34       $603.0319   $603.03   $603.00   $603.00