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	$166.68	3.415%	$172.3721	$172.37	$172.35	$172.40
Purchase #2	$53.42	7.474%	$57.4126	$57.41	$57.40	$57.40
Purchase #3	$67.58	7.240%	$72.4728	$72.47	$72.45	$72.50
Purchase #4	$42.51	11.719%	$47.4917	$47.49	$47.50	$47.50
Purchase #5	$30.77	7.300%	$33.0162	$33.02	$33.00	$33.00
Purchase #6	$167.56	3.575%	$173.5503	$173.55	$173.55	$173.60
Purchase #7	$223.43	4.721%	$233.9781	$233.98	$234.00	$234.00
7 purchase totals =	$751.95		$790.2938	$790.29	$790.25	$790.40