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	$164.71	11.301%	$183.3239	$183.32	$183.30	$183.30
Purchase #2	$221.27	5.475%	$233.3845	$233.38	$233.40	$233.40
Purchase #3	$238.72	7.108%	$255.6882	$255.69	$255.70	$255.70
Purchase #4	$118.80	5.478%	$125.3079	$125.31	$125.30	$125.30
Purchase #5	$197.90	5.493%	$208.7706	$208.77	$208.75	$208.80
Purchase #6	$174.62	4.561%	$182.5844	$182.58	$182.60	$182.60
Purchase #7	$37.45	12.599%	$42.1683	$42.17	$42.15	$42.20
7 purchase totals =	$1,153.47		$1,231.2278	$1,231.22	$1,231.20	$1,231.30