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	$226.89	10.104%	$249.815	$249.82	$249.80	$249.80
Purchase #2	$80.58	11.810%	$90.0965	$90.10	$90.10	$90.10
Purchase #3	$202.26	4.463%	$211.2869	$211.29	$211.30	$211.30
Purchase #4	$244.41	5.127%	$256.9409	$256.94	$256.95	$256.90
Purchase #5	$41.44	10.124%	$45.6354	$45.64	$45.65	$45.60
Purchase #6	$191.82	7.105%	$205.4488	$205.45	$205.45	$205.40
Purchase #7	$154.28	3.345%	$159.4407	$159.44	$159.45	$159.40
7 purchase totals =	$1,141.68		$1,218.6642	$1,218.68	$1,218.70	$1,218.50