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 $62.38   5.805%   $66.0012   $66.00   $66.00   $66.00  
  Purchase #2 $164.30   12.123%   $184.2181   $184.22   $184.20   $184.20  
  Purchase #3 $166.68   6.289%   $177.1625   $177.16   $177.15   $177.20  
  Purchase #4 $235.85   4.105%   $245.5316   $245.53   $245.55   $245.50  
  Purchase #5 $147.26   7.829%   $158.789   $158.79   $158.80   $158.80  
  Purchase #6 $166.42   7.486%   $178.8782   $178.88   $178.90   $178.90  
  Purchase #7 $242.46   12.451%   $272.6487   $272.65   $272.65   $272.60  
  7 purchase totals = $1,185.35       $1,283.2293   $1,283.23   $1,283.25   $1,283.20