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 $32.41   7.402%   $34.809   $34.81   $34.80   $34.80  
  Purchase #2 $130.30   4.650%   $136.359   $136.36   $136.35   $136.40  
  Purchase #3 $120.89   4.315%   $126.1064   $126.11   $126.10   $126.10  
  Purchase #4 $242.38   9.592%   $265.6291   $265.63   $265.65   $265.60  
  Purchase #5 $9.84   9.380%   $10.763   $10.76   $10.75   $10.80  
  Purchase #6 $49.73   5.372%   $52.4015   $52.40   $52.40   $52.40  
  Purchase #7 $42.97   9.673%   $47.1265   $47.13   $47.15   $47.10  
  7 purchase totals = $628.52       $673.1945   $673.20   $673.20   $673.20