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	$40.25	11.836%	$45.014	$45.01	$45.00	$45.00
Purchase #2	$179.44	6.207%	$190.5778	$190.58	$190.60	$190.60
Purchase #3	$56.80	4.279%	$59.2305	$59.23	$59.25	$59.20
Purchase #4	$49.43	13.177%	$55.9434	$55.94	$55.95	$55.90
Purchase #5	$152.73	3.707%	$158.3917	$158.39	$158.40	$158.40
Purchase #6	$211.76	5.257%	$222.8922	$222.89	$222.90	$222.90
Purchase #7	$129.96	11.831%	$145.3356	$145.34	$145.35	$145.30
7 purchase totals =	$820.37		$877.3852	$877.38	$877.45	$877.30