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	$239.50	4.547%	$250.3901	$250.39	$250.40	$250.40
Purchase #2	$101.54	3.635%	$105.231	$105.23	$105.25	$105.20
Purchase #3	$56.40	4.823%	$59.1202	$59.12	$59.10	$59.10
Purchase #4	$117.42	6.517%	$125.0723	$125.07	$125.05	$125.10
Purchase #5	$20.82	6.719%	$22.2189	$22.22	$22.20	$22.20
Purchase #6	$48.71	5.536%	$51.4066	$51.41	$51.40	$51.40
Purchase #7	$220.74	4.685%	$231.0817	$231.08	$231.10	$231.10
7 purchase totals =	$805.13		$844.5208	$844.52	$844.50	$844.50