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 $84.71   9.501%   $92.7583   $92.76   $92.75   $92.80  
  Purchase #2 $154.37   3.106%   $159.1647   $159.16   $159.15   $159.20  
  Purchase #3 $34.55   6.245%   $36.7076   $36.71   $36.70   $36.70  
  Purchase #4 $214.26   9.800%   $235.2575   $235.26   $235.25   $235.30  
  Purchase #5 $156.92   13.728%   $178.462   $178.46   $178.45   $178.50  
  Purchase #6 $218.30   13.682%   $248.1678   $248.17   $248.15   $248.20  
  Purchase #7 $116.51   5.817%   $123.2874   $123.29   $123.30   $123.30  
  7 purchase totals = $979.62       $1,073.8053   $1,073.81   $1,073.75   $1,074.00