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 $224.92   10.678%   $248.937   $248.94   $248.95   $248.90  
  Purchase #2 $118.38   6.171%   $125.6852   $125.69   $125.70   $125.70  
  Purchase #3 $176.52   3.245%   $182.2481   $182.25   $182.25   $182.20  
  Purchase #4 $15.60   13.683%   $17.7345   $17.73   $17.75   $17.70  
  Purchase #5 $57.53   10.492%   $63.566   $63.57   $63.55   $63.60  
  Purchase #6 $111.50   12.862%   $125.8411   $125.84   $125.85   $125.80  
  Purchase #7 $183.68   7.655%   $197.7407   $197.74   $197.75   $197.70  
  7 purchase totals = $888.13       $961.7526   $961.76   $961.80   $961.60