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 $98.34   5.753%   $103.9975   $104.00   $104.00   $104.00  
  Purchase #2 $199.82   13.174%   $226.1443   $226.14   $226.15   $226.10  
  Purchase #3 $110.94   12.349%   $124.64   $124.64   $124.65   $124.60  
  Purchase #4 $34.36   7.375%   $36.8941   $36.89   $36.90   $36.90  
  Purchase #5 $141.97   6.454%   $151.1327   $151.13   $151.15   $151.10  
  Purchase #6 $57.79   4.497%   $60.3888   $60.39   $60.40   $60.40  
  Purchase #7 $149.40   8.429%   $161.9929   $161.99   $162.00   $162.00  
  7 purchase totals = $792.62       $865.1903   $865.18   $865.25   $865.10