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 $241.98   9.318%   $264.5277   $264.53   $264.55   $264.50  
  Purchase #2 $14.78   9.784%   $16.2261   $16.23   $16.25   $16.20  
  Purchase #3 $86.38   13.571%   $98.1026   $98.10   $98.10   $98.10  
  Purchase #4 $114.86   13.841%   $130.7578   $130.76   $130.75   $130.80  
  Purchase #5 $201.69   8.427%   $218.6864   $218.69   $218.70   $218.70  
  Purchase #6 $234.75   13.738%   $267   $267.00   $267.00   $267.00  
  Purchase #7 $178.53   8.731%   $194.1175   $194.12   $194.10   $194.10  
  7 purchase totals = $1,072.97       $1,189.4181   $1,189.43   $1,189.45   $1,189.40