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	$55.39	10.123%	$60.9971	$61.00	$61.00	$61.00
Purchase #2	$75.72	4.169%	$78.8768	$78.88	$78.90	$78.90
Purchase #3	$36.86	12.461%	$41.4531	$41.45	$41.45	$41.50
Purchase #4	$89.60	10.569%	$99.0698	$99.07	$99.05	$99.10
Purchase #5	$128.75	10.412%	$142.1555	$142.16	$142.15	$142.20
Purchase #6	$24.43	9.819%	$26.8288	$26.83	$26.85	$26.80
Purchase #7	$183.27	12.369%	$205.9387	$205.94	$205.95	$205.90
7 purchase totals =	$594.02		$655.3198	$655.33	$655.35	$655.40