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 $238.55   10.141%   $262.7414   $262.74   $262.75   $262.70  
  Purchase #2 $167.46   5.833%   $177.2279   $177.23   $177.25   $177.20  
  Purchase #3 $53.38   10.103%   $58.773   $58.77   $58.75   $58.80  
  Purchase #4 $36.35   5.486%   $38.3442   $38.34   $38.35   $38.30  
  Purchase #5 $143.27   3.460%   $148.2271   $148.23   $148.25   $148.20  
  Purchase #6 $195.35   10.490%   $215.8422   $215.84   $215.85   $215.80  
  Purchase #7 $131.91   6.161%   $140.037   $140.04   $140.05   $140.00  
  7 purchase totals = $966.27       $1,041.1928   $1,041.19   $1,041.25   $1,041.00