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 $229.62   4.386%   $239.6911   $239.69   $239.70   $239.70  
  Purchase #2 $194.74   11.194%   $216.5392   $216.54   $216.55   $216.50  
  Purchase #3 $23.88   5.287%   $25.1425   $25.14   $25.15   $25.10  
  Purchase #4 $73.50   3.367%   $75.9747   $75.97   $75.95   $76.00  
  Purchase #5 $149.67   6.675%   $159.6605   $159.66   $159.65   $159.70  
  Purchase #6 $244.92   5.744%   $258.9882   $258.99   $259.00   $259.00  
  Purchase #7 $181.57   13.482%   $206.0493   $206.05   $206.05   $206.00  
  7 purchase totals = $1,097.90       $1,182.0455   $1,182.04   $1,182.05   $1,182.00