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 $122.46   11.420%   $136.4449   $136.44   $136.45   $136.40  
  Purchase #2 $94.82   10.556%   $104.8292   $104.83   $104.85   $104.80  
  Purchase #3 $93.76   3.519%   $97.0594   $97.06   $97.05   $97.10  
  Purchase #4 $67.58   8.743%   $73.4885   $73.49   $73.50   $73.50  
  Purchase #5 $76.49   10.477%   $84.5039   $84.50   $84.50   $84.50  
  Purchase #6 $65.29   11.353%   $72.7024   $72.70   $72.70   $72.70  
  Purchase #7 $171.39   9.294%   $187.319   $187.32   $187.30   $187.30  
  7 purchase totals = $691.79       $756.3473   $756.34   $756.35   $756.30