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	$97.66	9.474%	$106.9123	$106.91	$106.90	$106.90
Purchase #2	$76.30	12.354%	$85.7261	$85.73	$85.75	$85.70
Purchase #3	$50.69	10.593%	$56.0596	$56.06	$56.05	$56.10
Purchase #4	$37.58	4.551%	$39.2903	$39.29	$39.30	$39.30
Purchase #5	$13.52	4.620%	$14.1446	$14.14	$14.15	$14.10
Purchase #6	$113.33	4.325%	$118.2315	$118.23	$118.25	$118.20
Purchase #7	$93.50	13.288%	$105.9243	$105.92	$105.90	$105.90
7 purchase totals =	$482.58		$526.2887	$526.28	$526.30	$526.20