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 $202.57   10.606%   $224.0546   $224.05   $224.05   $224.10  
  Purchase #2 $88.73   12.430%   $99.7591   $99.76   $99.75   $99.80  
  Purchase #3 $225.59   5.401%   $237.7741   $237.77   $237.75   $237.80  
  Purchase #4 $244.69   4.661%   $256.095   $256.10   $256.10   $256.10  
  Purchase #5 $236.76   8.509%   $256.9059   $256.91   $256.90   $256.90  
  Purchase #6 $213.64   9.176%   $233.2436   $233.24   $233.25   $233.20  
  Purchase #7 $135.53   8.238%   $146.695   $146.70   $146.70   $146.70  
  7 purchase totals = $1,347.51       $1,454.5273   $1,454.53   $1,454.50   $1,454.60