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 $227.44   11.339%   $253.2294   $253.23   $253.25   $253.20  
  Purchase #2 $92.34   10.252%   $101.8067   $101.81   $101.80   $101.80  
  Purchase #3 $112.42   11.410%   $125.2471   $125.25   $125.25   $125.20  
  Purchase #4 $238.29   4.160%   $248.2029   $248.20   $248.20   $248.20  
  Purchase #5 $231.79   13.297%   $262.6111   $262.61   $262.60   $262.60  
  Purchase #6 $46.41   3.816%   $48.181   $48.18   $48.20   $48.20  
  Purchase #7 $88.69   5.383%   $93.4642   $93.46   $93.45   $93.50  
  7 purchase totals = $1,037.38       $1,132.7424   $1,132.74   $1,132.75   $1,132.70