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	$103.83	6.168%	$110.2342	$110.23	$110.25	$110.20
Purchase #2	$140.88	11.603%	$157.2263	$157.23	$157.25	$157.20
Purchase #3	$246.51	11.460%	$274.76	$274.76	$274.75	$274.80
Purchase #4	$49.74	11.103%	$55.2626	$55.26	$55.25	$55.30
Purchase #5	$146.49	3.299%	$151.3227	$151.32	$151.30	$151.30
Purchase #6	$55.75	8.438%	$60.4542	$60.45	$60.45	$60.50
Purchase #7	$86.58	4.793%	$90.7298	$90.73	$90.75	$90.70
7 purchase totals =	$829.78		$899.9898	$899.98	$900.00	$900.00