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	$143.27	9.453%	$156.8133	$156.81	$156.80	$156.80
Purchase #2	$164.39	11.830%	$183.8373	$183.84	$183.85	$183.80
Purchase #3	$18.73	7.222%	$20.0827	$20.08	$20.10	$20.10
Purchase #4	$40.94	10.334%	$45.1707	$45.17	$45.15	$45.20
Purchase #5	$9.77	13.201%	$11.0597	$11.06	$11.05	$11.10
Purchase #6	$215.63	10.732%	$238.7714	$238.77	$238.75	$238.80
Purchase #7	$211.99	4.825%	$222.2185	$222.22	$222.20	$222.20
7 purchase totals =	$804.72		$877.9536	$877.95	$877.90	$878.00