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	$229.33	9.825%	$251.8617	$251.86	$251.85	$251.90
Purchase #2	$36.79	12.602%	$41.4263	$41.43	$41.45	$41.40
Purchase #3	$79.61	13.400%	$90.2777	$90.28	$90.30	$90.30
Purchase #4	$44.73	8.115%	$48.3598	$48.36	$48.35	$48.40
Purchase #5	$68.30	4.328%	$71.256	$71.26	$71.25	$71.30
Purchase #6	$59.37	3.483%	$61.4379	$61.44	$61.45	$61.40
Purchase #7	$145.68	6.242%	$154.7733	$154.77	$154.75	$154.80
7 purchase totals =	$663.81		$719.3927	$719.40	$719.40	$719.50