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 $233.62   6.819%   $249.5505   $249.55   $249.55   $249.60  
  Purchase #2 $225.72   13.384%   $255.9304   $255.93   $255.95   $255.90  
  Purchase #3 $220.96   4.735%   $231.4225   $231.42   $231.40   $231.40  
  Purchase #4 $84.91   13.218%   $96.1334   $96.13   $96.15   $96.10  
  Purchase #5 $118.62   7.854%   $127.9364   $127.94   $127.95   $127.90  
  Purchase #6 $124.30   8.869%   $135.3242   $135.32   $135.30   $135.30  
  Purchase #7 $237.38   7.788%   $255.8672   $255.87   $255.85   $255.90  
  7 purchase totals = $1,245.51       $1,352.1646   $1,352.16   $1,352.15   $1,352.10