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 $61.31   5.140%   $64.4613   $64.46   $64.45   $64.50  
  Purchase #2 $131.73   5.599%   $139.1056   $139.11   $139.10   $139.10  
  Purchase #3 $250.92   8.427%   $272.065   $272.07   $272.05   $272.10  
  Purchase #4 $49.81   11.404%   $55.4903   $55.49   $55.50   $55.50  
  Purchase #5 $114.45   4.672%   $119.7971   $119.80   $119.80   $119.80  
  Purchase #6 $244.38   3.863%   $253.8204   $253.82   $253.80   $253.80  
  Purchase #7 $31.52   9.570%   $34.5365   $34.54   $34.55   $34.50  
  7 purchase totals = $884.12       $939.2762   $939.29   $939.25   $939.30