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	$29.86	4.501%	$31.204	$31.20	$31.20	$31.20
Purchase #2	$14.29	7.358%	$15.3415	$15.34	$15.35	$15.30
Purchase #3	$173.55	13.294%	$196.6217	$196.62	$196.60	$196.60
Purchase #4	$192.45	12.445%	$216.4004	$216.40	$216.40	$216.40
Purchase #5	$239.73	8.497%	$260.0999	$260.10	$260.10	$260.10
Purchase #6	$153.78	11.205%	$171.011	$171.01	$171.00	$171.00
Purchase #7	$123.44	5.660%	$130.4267	$130.43	$130.45	$130.40
7 purchase totals =	$927.10		$1,021.1052	$1,021.10	$1,021.10	$1,021.00