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	$85.92	5.579%	$90.7135	$90.71	$90.70	$90.70
Purchase #2	$146.49	13.151%	$165.7549	$165.75	$165.75	$165.80
Purchase #3	$107.48	3.620%	$111.3708	$111.37	$111.35	$111.40
Purchase #4	$126.70	4.263%	$132.1012	$132.10	$132.10	$132.10
Purchase #5	$80.84	10.811%	$89.5796	$89.58	$89.60	$89.60
Purchase #6	$28.76	13.494%	$32.6409	$32.64	$32.65	$32.60
Purchase #7	$37.48	5.327%	$39.4766	$39.48	$39.50	$39.50
7 purchase totals =	$613.67		$661.6375	$661.63	$661.65	$661.70