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 $235.49   11.657%   $262.9411   $262.94   $262.95   $262.90  
  Purchase #2 $118.92   5.564%   $125.5367   $125.54   $125.55   $125.50  
  Purchase #3 $58.51   11.497%   $65.2369   $65.24   $65.25   $65.20  
  Purchase #4 $222.31   13.300%   $251.8772   $251.88   $251.90   $251.90  
  Purchase #5 $219.31   7.345%   $235.4183   $235.42   $235.40   $235.40  
  Purchase #6 $109.82   4.142%   $114.3687   $114.37   $114.35   $114.40  
  Purchase #7 $164.55   11.811%   $183.985   $183.99   $184.00   $184.00  
  7 purchase totals = $1,128.91       $1,239.3639   $1,239.38   $1,239.40   $1,239.30