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	$57.43	6.181%	$60.9797	$60.98	$61.00	$61.00
Purchase #2	$110.55	13.216%	$125.1603	$125.16	$125.15	$125.20
Purchase #3	$172.37	11.103%	$191.5082	$191.51	$191.50	$191.50
Purchase #4	$124.39	13.745%	$141.4874	$141.49	$141.50	$141.50
Purchase #5	$97.54	10.501%	$107.7827	$107.78	$107.80	$107.80
Purchase #6	$136.46	3.721%	$141.5377	$141.54	$141.55	$141.50
Purchase #7	$79.69	3.217%	$82.2536	$82.25	$82.25	$82.30
7 purchase totals =	$778.43		$850.7096	$850.71	$850.75	$850.80