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 $225.44   3.485%   $233.2966   $233.30   $233.30   $233.30  
  Purchase #2 $40.45   11.358%   $45.0443   $45.04   $45.05   $45.00  
  Purchase #3 $50.48   12.165%   $56.6209   $56.62   $56.60   $56.60  
  Purchase #4 $190.71   9.298%   $208.4422   $208.44   $208.45   $208.40  
  Purchase #5 $211.51   3.187%   $218.2508   $218.25   $218.25   $218.30  
  Purchase #6 $219.94   12.869%   $248.2441   $248.24   $248.25   $248.20  
  Purchase #7 $245.92   5.177%   $258.6513   $258.65   $258.65   $258.70  
  7 purchase totals = $1,184.45       $1,268.5502   $1,268.54   $1,268.55   $1,268.50