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 $174.42   11.716%   $194.855   $194.86   $194.85   $194.90  
  Purchase #2 $184.64   11.537%   $205.9419   $205.94   $205.95   $205.90  
  Purchase #3 $225.58   8.713%   $245.2348   $245.23   $245.25   $245.20  
  Purchase #4 $7.48   10.267%   $8.248   $8.25   $8.25   $8.20  
  Purchase #5 $173.38   12.729%   $195.4495   $195.45   $195.45   $195.40  
  Purchase #6 $197.64   12.449%   $222.2442   $222.24   $222.25   $222.20  
  Purchase #7 $65.68   10.697%   $72.7058   $72.71   $72.70   $72.70  
  7 purchase totals = $1,028.82       $1,144.6792   $1,144.68   $1,144.70   $1,144.50