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 $54.44   4.141%   $56.6944   $56.69   $56.70   $56.70  
  Purchase #2 $81.95   12.646%   $92.3134   $92.31   $92.30   $92.30  
  Purchase #3 $100.88   9.507%   $110.4707   $110.47   $110.45   $110.50  
  Purchase #4 $105.76   5.162%   $111.2193   $111.22   $111.20   $111.20  
  Purchase #5 $196.93   6.496%   $209.7226   $209.72   $209.70   $209.70  
  Purchase #6 $94.53   4.464%   $98.7498   $98.75   $98.75   $98.70  
  Purchase #7 $104.34   11.167%   $115.9916   $115.99   $116.00   $116.00  
  7 purchase totals = $738.83       $795.1618   $795.15   $795.10   $795.10