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 $50.87   7.852%   $54.8643   $54.86   $54.85   $54.90  
  Purchase #2 $238.77   4.301%   $249.0395   $249.04   $249.05   $249.00  
  Purchase #3 $34.79   4.592%   $36.3876   $36.39   $36.40   $36.40  
  Purchase #4 $30.62   12.856%   $34.5565   $34.56   $34.55   $34.60  
  Purchase #5 $243.94   9.727%   $267.668   $267.67   $267.65   $267.70  
  Purchase #6 $237.50   9.233%   $259.4284   $259.43   $259.45   $259.40  
  Purchase #7 $197.38   9.677%   $216.4805   $216.48   $216.50   $216.50  
  7 purchase totals = $1,033.87       $1,118.4248   $1,118.43   $1,118.45   $1,118.50