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	$99.57	11.785%	$111.3043	$111.30	$111.30	$111.30
Purchase #2	$131.30	10.653%	$145.2874	$145.29	$145.30	$145.30
Purchase #3	$130.59	5.759%	$138.1107	$138.11	$138.10	$138.10
Purchase #4	$175.44	9.257%	$191.6805	$191.68	$191.70	$191.70
Purchase #5	$214.94	6.658%	$229.2507	$229.25	$229.25	$229.30
Purchase #6	$85.64	5.409%	$90.2723	$90.27	$90.25	$90.30
Purchase #7	$80.91	12.178%	$90.7632	$90.76	$90.75	$90.80
7 purchase totals =	$918.39		$996.6691	$996.66	$996.65	$996.80