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 $248.82   7.406%   $267.2476   $267.25   $267.25   $267.20  
  Purchase #2 $219.37   8.656%   $238.3587   $238.36   $238.35   $238.40  
  Purchase #3 $129.28   7.660%   $139.1828   $139.18   $139.20   $139.20  
  Purchase #4 $192.99   13.583%   $219.2038   $219.20   $219.20   $219.20  
  Purchase #5 $208.76   5.112%   $219.4318   $219.43   $219.45   $219.40  
  Purchase #6 $34.74   5.559%   $36.6712   $36.67   $36.65   $36.70  
  Purchase #7 $225.26   6.339%   $239.5392   $239.54   $239.55   $239.50  
  7 purchase totals = $1,259.22       $1,359.6351   $1,359.63   $1,359.65   $1,359.60