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 $235.26   13.808%   $267.7447   $267.74   $267.75   $267.70  
  Purchase #2 $249.57   3.839%   $259.151   $259.15   $259.15   $259.20  
  Purchase #3 $185.54   11.426%   $206.7398   $206.74   $206.75   $206.70  
  Purchase #4 $144.79   3.171%   $149.3813   $149.38   $149.40   $149.40  
  Purchase #5 $229.99   10.306%   $253.6928   $253.69   $253.70   $253.70  
  Purchase #6 $177.61   10.207%   $195.7387   $195.74   $195.75   $195.70  
  Purchase #7 $91.64   13.810%   $104.2955   $104.30   $104.30   $104.30  
  7 purchase totals = $1,314.40       $1,436.7438   $1,436.74   $1,436.80   $1,436.70