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	$30.63	9.427%	$33.5175	$33.52	$33.50	$33.50
Purchase #2	$104.43	5.530%	$110.205	$110.21	$110.20	$110.20
Purchase #3	$9.85	11.376%	$10.9705	$10.97	$10.95	$11.00
Purchase #4	$158.77	6.762%	$169.506	$169.51	$169.50	$169.50
Purchase #5	$143.66	5.684%	$151.8256	$151.83	$151.85	$151.80
Purchase #6	$56.83	13.216%	$64.3407	$64.34	$64.35	$64.30
Purchase #7	$54.88	12.663%	$61.8295	$61.83	$61.85	$61.80
7 purchase totals =	$559.05		$602.1948	$602.21	$602.20	$602.10