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 $191.76   13.802%   $218.2267   $218.23   $218.25   $218.20  
  Purchase #2 $72.87   4.618%   $76.2351   $76.24   $76.25   $76.20  
  Purchase #3 $166.48   12.331%   $187.0086   $187.01   $187.00   $187.00  
  Purchase #4 $95.96   8.753%   $104.3594   $104.36   $104.35   $104.40  
  Purchase #5 $28.35   5.730%   $29.9745   $29.97   $29.95   $30.00  
  Purchase #6 $101.75   10.798%   $112.737   $112.74   $112.75   $112.70  
  Purchase #7 $49.96   13.475%   $56.6921   $56.69   $56.70   $56.70  
  7 purchase totals = $707.13       $785.2334   $785.24   $785.25   $785.20