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 $245.51   12.366%   $275.8698   $275.87   $275.85   $275.90  
  Purchase #2 $233.74   12.663%   $263.3385   $263.34   $263.35   $263.30  
  Purchase #3 $142.69   7.391%   $153.2362   $153.24   $153.25   $153.20  
  Purchase #4 $149.31   6.720%   $159.3436   $159.34   $159.35   $159.30  
  Purchase #5 $207.63   8.676%   $225.644   $225.64   $225.65   $225.60  
  Purchase #6 $131.83   8.149%   $142.5728   $142.57   $142.55   $142.60  
  Purchase #7 $8.41   4.259%   $8.7682   $8.77   $8.75   $8.80  
  7 purchase totals = $1,119.12       $1,228.7731   $1,228.77   $1,228.75   $1,228.70