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 $67.37   6.762%   $71.9256   $71.93   $71.95   $71.90  
  Purchase #2 $174.82   9.486%   $191.4034   $191.40   $191.40   $191.40  
  Purchase #3 $98.66   4.732%   $103.3286   $103.33   $103.35   $103.30  
  Purchase #4 $124.93   3.637%   $129.4737   $129.47   $129.45   $129.50  
  Purchase #5 $85.30   8.677%   $92.7015   $92.70   $92.70   $92.70  
  Purchase #6 $102.86   12.185%   $115.3935   $115.39   $115.40   $115.40  
  Purchase #7 $133.38   9.194%   $145.643   $145.64   $145.65   $145.60  
  7 purchase totals = $787.32       $849.8693   $849.86   $849.90   $849.80