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 $203.87   8.364%   $220.9217   $220.92   $220.90   $220.90  
  Purchase #2 $190.31   13.394%   $215.8001   $215.80   $215.80   $215.80  
  Purchase #3 $58.61   10.175%   $64.5736   $64.57   $64.55   $64.60  
  Purchase #4 $158.53   3.604%   $164.2434   $164.24   $164.25   $164.20  
  Purchase #5 $15.30   4.151%   $15.9351   $15.94   $15.95   $15.90  
  Purchase #6 $133.36   13.628%   $151.5343   $151.53   $151.55   $151.50  
  Purchase #7 $198.39   12.649%   $223.4844   $223.48   $223.50   $223.50  
  7 purchase totals = $958.37       $1,056.4926   $1,056.48   $1,056.50   $1,056.40