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 $83.38   12.664%   $93.9392   $93.94   $93.95   $93.90  
  Purchase #2 $173.68   12.485%   $195.3639   $195.36   $195.35   $195.40  
  Purchase #3 $76.79   7.160%   $82.2882   $82.29   $82.30   $82.30  
  Purchase #4 $36.82   12.816%   $41.5389   $41.54   $41.55   $41.50  
  Purchase #5 $162.32   8.448%   $176.0328   $176.03   $176.05   $176.00  
  Purchase #6 $101.51   7.769%   $109.3963   $109.40   $109.40   $109.40  
  Purchase #7 $172.72   3.444%   $178.6685   $178.67   $178.65   $178.70  
  7 purchase totals = $807.22       $877.2278   $877.23   $877.25   $877.20