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 $237.29   12.538%   $267.0414   $267.04   $267.05   $267.00  
  Purchase #2 $31.92   13.539%   $36.2416   $36.24   $36.25   $36.20  
  Purchase #3 $48.89   6.593%   $52.1133   $52.11   $52.10   $52.10  
  Purchase #4 $166.42   5.233%   $175.1288   $175.13   $175.15   $175.10  
  Purchase #5 $125.48   4.105%   $130.631   $130.63   $130.65   $130.60  
  Purchase #6 $47.49   6.603%   $50.6258   $50.63   $50.65   $50.60  
  Purchase #7 $225.47   4.400%   $235.3907   $235.39   $235.40   $235.40  
  7 purchase totals = $882.96       $947.1726   $947.17   $947.25   $947.00