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 $49.26   10.193%   $54.2811   $54.28   $54.30   $54.30  
  Purchase #2 $44.71   10.379%   $49.3505   $49.35   $49.35   $49.40  
  Purchase #3 $164.35   8.605%   $178.4923   $178.49   $178.50   $178.50  
  Purchase #4 $29.93   13.717%   $34.0355   $34.04   $34.05   $34.00  
  Purchase #5 $175.57   7.295%   $188.3778   $188.38   $188.40   $188.40  
  Purchase #6 $236.94   3.370%   $244.9249   $244.92   $244.90   $244.90  
  Purchase #7 $243.62   12.214%   $273.3757   $273.38   $273.40   $273.40  
  7 purchase totals = $944.38       $1,022.8378   $1,022.84   $1,022.90   $1,022.90