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 $217.44   11.422%   $242.276   $242.28   $242.30   $242.30  
  Purchase #2 $119.35   6.233%   $126.7891   $126.79   $126.80   $126.80  
  Purchase #3 $84.89   11.265%   $94.4529   $94.45   $94.45   $94.50  
  Purchase #4 $57.57   4.873%   $60.3754   $60.38   $60.40   $60.40  
  Purchase #5 $16.45   6.409%   $17.5043   $17.50   $17.50   $17.50  
  Purchase #6 $239.51   5.818%   $253.4447   $253.44   $253.45   $253.40  
  Purchase #7 $79.66   8.202%   $86.1937   $86.19   $86.20   $86.20  
  7 purchase totals = $814.87       $881.0361   $881.03   $881.10   $881.10