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 $110.81   13.689%   $125.9788   $125.98   $126.00   $126.00  
  Purchase #2 $67.48   5.436%   $71.1482   $71.15   $71.15   $71.10  
  Purchase #3 $226.31   10.443%   $249.9436   $249.94   $249.95   $249.90  
  Purchase #4 $116.83   11.267%   $129.9932   $129.99   $130.00   $130.00  
  Purchase #5 $24.84   3.198%   $25.6344   $25.63   $25.65   $25.60  
  Purchase #6 $245.93   9.672%   $269.7163   $269.72   $269.70   $269.70  
  Purchase #7 $76.67   8.497%   $83.1846   $83.18   $83.20   $83.20  
  7 purchase totals = $868.87       $955.5991   $955.59   $955.65   $955.50