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 $134.65   8.577%   $146.1989   $146.20   $146.20   $146.20  
  Purchase #2 $142.29   6.703%   $151.8277   $151.83   $151.85   $151.80  
  Purchase #3 $124.72   4.763%   $130.6604   $130.66   $130.65   $130.70  
  Purchase #4 $190.63   13.511%   $216.386   $216.39   $216.40   $216.40  
  Purchase #5 $127.90   10.527%   $141.364   $141.36   $141.35   $141.40  
  Purchase #6 $13.56   8.171%   $14.668   $14.67   $14.65   $14.70  
  Purchase #7 $209.75   6.601%   $223.5956   $223.60   $223.60   $223.60  
  7 purchase totals = $943.50       $1,024.7006   $1,024.71   $1,024.70   $1,024.80