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	$38.97	12.284%	$43.7571	$43.76	$43.75	$43.80
Purchase #2	$165.73	4.163%	$172.6293	$172.63	$172.65	$172.60
Purchase #3	$53.53	8.133%	$57.8836	$57.88	$57.90	$57.90
Purchase #4	$240.42	5.622%	$253.9364	$253.94	$253.95	$253.90
Purchase #5	$105.29	3.765%	$109.2542	$109.25	$109.25	$109.30
Purchase #6	$173.84	4.361%	$181.4212	$181.42	$181.40	$181.40
Purchase #7	$244.82	5.447%	$258.1553	$258.16	$258.15	$258.20
7 purchase totals =	$1,022.60		$1,077.0371	$1,077.04	$1,077.05	$1,077.10