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 $9.27   6.494%   $9.872   $9.87   $9.85   $9.90  
  Purchase #2 $190.86   11.543%   $212.891   $212.89   $212.90   $212.90  
  Purchase #3 $29.80   5.675%   $31.4912   $31.49   $31.50   $31.50  
  Purchase #4 $132.81   5.582%   $140.2235   $140.22   $140.20   $140.20  
  Purchase #5 $92.99   5.122%   $97.7529   $97.75   $97.75   $97.80  
  Purchase #6 $26.64   4.564%   $27.8558   $27.86   $27.85   $27.90  
  Purchase #7 $124.56   12.667%   $140.338   $140.34   $140.35   $140.30  
  7 purchase totals = $606.93       $660.4244   $660.42   $660.40   $660.50