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 $73.29   12.873%   $82.7246   $82.72   $82.70   $82.70  
  Purchase #2 $92.79   4.209%   $96.6955   $96.70   $96.70   $96.70  
  Purchase #3 $62.86   3.222%   $64.8853   $64.89   $64.90   $64.90  
  Purchase #4 $5.38   13.494%   $6.106   $6.11   $6.10   $6.10  
  Purchase #5 $166.81   8.308%   $180.6686   $180.67   $180.65   $180.70  
  Purchase #6 $196.79   12.480%   $221.3494   $221.35   $221.35   $221.30  
  Purchase #7 $226.72   12.201%   $254.3821   $254.38   $254.40   $254.40  
  7 purchase totals = $824.64       $906.8115   $906.82   $906.80   $906.80