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 $58.44   9.865%   $64.2051   $64.21   $64.20   $64.20  
  Purchase #2 $94.60   9.820%   $103.8897   $103.89   $103.90   $103.90  
  Purchase #3 $56.80   13.541%   $64.4913   $64.49   $64.50   $64.50  
  Purchase #4 $60.31   3.596%   $62.4787   $62.48   $62.50   $62.50  
  Purchase #5 $119.60   7.125%   $128.1215   $128.12   $128.10   $128.10  
  Purchase #6 $172.87   5.465%   $182.3173   $182.32   $182.30   $182.30  
  Purchase #7 $145.59   11.581%   $162.4508   $162.45   $162.45   $162.50  
  7 purchase totals = $708.21       $767.9544   $767.96   $767.95   $768.00