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 $32.58   5.671%   $34.4276   $34.43   $34.45   $34.40  
  Purchase #2 $113.86   13.549%   $129.2869   $129.29   $129.30   $129.30  
  Purchase #3 $185.47   9.310%   $202.7373   $202.74   $202.75   $202.70  
  Purchase #4 $157.68   5.864%   $166.9264   $166.93   $166.95   $166.90  
  Purchase #5 $249.63   12.666%   $281.2481   $281.25   $281.25   $281.20  
  Purchase #6 $86.68   6.568%   $92.3731   $92.37   $92.35   $92.40  
  Purchase #7 $59.71   4.161%   $62.1945   $62.19   $62.20   $62.20  
  7 purchase totals = $885.61       $969.1939   $969.20   $969.25   $969.10