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 $55.28   13.190%   $62.5714   $62.57   $62.55   $62.60  
  Purchase #2 $249.27   12.328%   $280   $280.00   $280.00   $280.00  
  Purchase #3 $106.25   3.551%   $110.0229   $110.02   $110.00   $110.00  
  Purchase #4 $183.31   6.519%   $195.26   $195.26   $195.25   $195.30  
  Purchase #5 $38.26   10.239%   $42.1774   $42.18   $42.20   $42.20  
  Purchase #6 $105.90   13.781%   $120.4941   $120.49   $120.50   $120.50  
  Purchase #7 $48.69   6.387%   $51.7998   $51.80   $51.80   $51.80  
  7 purchase totals = $786.96       $862.3256   $862.32   $862.30   $862.40