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	$134.52	11.682%	$150.2346	$150.23	$150.25	$150.20
Purchase #2	$199.89	11.762%	$223.4011	$223.40	$223.40	$223.40
Purchase #3	$58.39	13.698%	$66.3883	$66.39	$66.40	$66.40
Purchase #4	$188.53	12.404%	$211.9153	$211.92	$211.90	$211.90
Purchase #5	$208.55	10.349%	$230.1328	$230.13	$230.15	$230.10
Purchase #6	$250.44	6.379%	$266.4156	$266.42	$266.40	$266.40
Purchase #7	$134.32	10.114%	$147.9051	$147.91	$147.90	$147.90
7 purchase totals =	$1,174.64		$1,296.3928	$1,296.40	$1,296.40	$1,296.30