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 $49.64   12.778%   $55.983   $55.98   $56.00   $56.00  
  Purchase #2 $61.86   10.827%   $68.5576   $68.56   $68.55   $68.60  
  Purchase #3 $193.71   8.492%   $210.1599   $210.16   $210.15   $210.20  
  Purchase #4 $62.88   11.302%   $69.9867   $69.99   $70.00   $70.00  
  Purchase #5 $237.74   3.434%   $245.904   $245.90   $245.90   $245.90  
  Purchase #6 $175.94   8.487%   $190.872   $190.87   $190.85   $190.90  
  Purchase #7 $15.60   4.450%   $16.2942   $16.29   $16.30   $16.30  
  7 purchase totals = $797.37       $857.7574   $857.75   $857.75   $857.90