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 $78.61   8.443%   $85.247   $85.25   $85.25   $85.20  
  Purchase #2 $95.59   11.751%   $106.8228   $106.82   $106.80   $106.80  
  Purchase #3 $187.36   13.137%   $211.9735   $211.97   $211.95   $212.00  
  Purchase #4 $119.65   11.660%   $133.6012   $133.60   $133.60   $133.60  
  Purchase #5 $94.73   10.776%   $104.9381   $104.94   $104.95   $104.90  
  Purchase #6 $13.68   11.265%   $15.2211   $15.22   $15.20   $15.20  
  Purchase #7 $165.75   13.532%   $188.1793   $188.18   $188.20   $188.20  
  7 purchase totals = $755.37       $845.9830   $845.98   $845.95   $845.90