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 $76.48   11.846%   $85.5398   $85.54   $85.55   $85.50  
  Purchase #2 $203.92   6.762%   $217.7091   $217.71   $217.70   $217.70  
  Purchase #3 $226.90   6.296%   $241.1856   $241.19   $241.20   $241.20  
  Purchase #4 $33.35   9.766%   $36.607   $36.61   $36.60   $36.60  
  Purchase #5 $237.39   10.535%   $262.399   $262.40   $262.40   $262.40  
  Purchase #6 $42.44   6.728%   $45.2954   $45.30   $45.30   $45.30  
  Purchase #7 $13.77   8.179%   $14.8962   $14.90   $14.90   $14.90  
  7 purchase totals = $834.25       $903.6321   $903.65   $903.65   $903.60