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 $67.63   11.624%   $75.4913   $75.49   $75.50   $75.50  
  Purchase #2 $116.34   7.415%   $124.9666   $124.97   $124.95   $125.00  
  Purchase #3 $83.86   8.695%   $91.1516   $91.15   $91.15   $91.20  
  Purchase #4 $44.66   7.164%   $47.8594   $47.86   $47.85   $47.90  
  Purchase #5 $44.77   3.140%   $46.1758   $46.18   $46.20   $46.20  
  Purchase #6 $124.59   5.796%   $131.8112   $131.81   $131.80   $131.80  
  Purchase #7 $120.61   5.376%   $127.094   $127.09   $127.10   $127.10  
  7 purchase totals = $602.46       $644.5499   $644.55   $644.55   $644.70