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 $244.27   9.504%   $267.4854   $267.49   $267.50   $267.50  
  Purchase #2 $182.29   13.114%   $206.1955   $206.20   $206.20   $206.20  
  Purchase #3 $86.56   11.376%   $96.4071   $96.41   $96.40   $96.40  
  Purchase #4 $241.88   10.589%   $267.4927   $267.49   $267.50   $267.50  
  Purchase #5 $9.85   11.169%   $10.9501   $10.95   $10.95   $11.00  
  Purchase #6 $238.27   9.722%   $261.4346   $261.43   $261.45   $261.40  
  Purchase #7 $191.69   12.804%   $216.234   $216.23   $216.25   $216.20  
  7 purchase totals = $1,194.81       $1,326.1994   $1,326.20   $1,326.25   $1,326.20