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 $245.32   11.491%   $273.5097   $273.51   $273.50   $273.50  
  Purchase #2 $114.69   3.445%   $118.6411   $118.64   $118.65   $118.60  
  Purchase #3 $76.63   5.861%   $81.1213   $81.12   $81.10   $81.10  
  Purchase #4 $230.38   7.611%   $247.9142   $247.91   $247.90   $247.90  
  Purchase #5 $189.95   11.804%   $212.3717   $212.37   $212.35   $212.40  
  Purchase #6 $184.73   9.445%   $202.1777   $202.18   $202.20   $202.20  
  Purchase #7 $84.47   13.727%   $96.0652   $96.07   $96.05   $96.10  
  7 purchase totals = $1,126.17       $1,231.8009   $1,231.80   $1,231.75   $1,231.80