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	$176.91	4.213%	$184.3632	$184.36	$184.35	$184.40
Purchase #2	$100.78	10.824%	$111.6884	$111.69	$111.70	$111.70
Purchase #3	$247.41	13.785%	$281.5155	$281.52	$281.50	$281.50
Purchase #4	$83.64	7.704%	$90.0836	$90.08	$90.10	$90.10
Purchase #5	$101.99	10.689%	$112.8917	$112.89	$112.90	$112.90
Purchase #6	$175.70	5.538%	$185.4303	$185.43	$185.45	$185.40
Purchase #7	$80.41	11.636%	$89.7665	$89.77	$89.75	$89.80
7 purchase totals =	$966.84		$1,055.7392	$1,055.74	$1,055.75	$1,055.80