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 $119.68   6.559%   $127.5298   $127.53   $127.55   $127.50  
  Purchase #2 $71.95   5.699%   $76.0504   $76.05   $76.05   $76.10  
  Purchase #3 $45.61   6.716%   $48.6732   $48.67   $48.65   $48.70  
  Purchase #4 $118.77   8.164%   $128.4664   $128.47   $128.45   $128.50  
  Purchase #5 $21.34   10.386%   $23.5564   $23.56   $23.55   $23.60  
  Purchase #6 $178.50   9.174%   $194.8756   $194.88   $194.90   $194.90  
  Purchase #7 $112.67   11.842%   $126.0124   $126.01   $126.00   $126.00  
  7 purchase totals = $668.52       $725.1642   $725.17   $725.15   $725.30