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 $70.69   6.461%   $75.2573   $75.26   $75.25   $75.30  
  Purchase #2 $128.64   13.772%   $146.3563   $146.36   $146.35   $146.40  
  Purchase #3 $175.36   10.728%   $194.1726   $194.17   $194.15   $194.20  
  Purchase #4 $60.99   10.494%   $67.3903   $67.39   $67.40   $67.40  
  Purchase #5 $206.42   12.866%   $232.978   $232.98   $233.00   $233.00  
  Purchase #6 $161.65   6.680%   $172.4482   $172.45   $172.45   $172.40  
  Purchase #7 $72.62   4.644%   $75.9925   $75.99   $76.00   $76.00  
  7 purchase totals = $876.37       $964.5952   $964.60   $964.60   $964.70