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 $83.64   13.541%   $94.9657   $94.97   $94.95   $95.00  
  Purchase #2 $48.46   10.200%   $53.4029   $53.40   $53.40   $53.40  
  Purchase #3 $211.45   4.468%   $220.8976   $220.90   $220.90   $220.90  
  Purchase #4 $14.65   9.555%   $16.0498   $16.05   $16.05   $16.00  
  Purchase #5 $93.99   5.734%   $99.3794   $99.38   $99.40   $99.40  
  Purchase #6 $172.48   11.465%   $192.2548   $192.25   $192.25   $192.30  
  Purchase #7 $101.46   9.239%   $110.8339   $110.83   $110.85   $110.80  
  7 purchase totals = $726.13       $787.7841   $787.78   $787.80   $787.80