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 $57.55   8.781%   $62.6035   $62.60   $62.60   $62.60  
  Purchase #2 $202.99   3.374%   $209.8389   $209.84   $209.85   $209.80  
  Purchase #3 $44.81   10.327%   $49.4375   $49.44   $49.45   $49.40  
  Purchase #4 $227.67   11.655%   $254.2049   $254.20   $254.20   $254.20  
  Purchase #5 $26.29   13.561%   $29.8552   $29.86   $29.85   $29.90  
  Purchase #6 $76.53   11.389%   $85.246   $85.25   $85.25   $85.20  
  Purchase #7 $134.99   13.601%   $153.35   $153.35   $153.35   $153.40  
  7 purchase totals = $770.83       $844.5360   $844.54   $844.55   $844.50