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	$66.61	7.342%	$71.5005	$71.50	$71.50	$71.50
Purchase #2	$48.79	5.513%	$51.4798	$51.48	$51.50	$51.50
Purchase #3	$111.64	8.163%	$120.7532	$120.75	$120.75	$120.80
Purchase #4	$29.52	11.417%	$32.8903	$32.89	$32.90	$32.90
Purchase #5	$177.38	7.146%	$190.0556	$190.06	$190.05	$190.10
Purchase #6	$12.29	11.171%	$13.6629	$13.66	$13.65	$13.70
Purchase #7	$211.33	8.304%	$228.8788	$228.88	$228.90	$228.90
7 purchase totals =	$657.56		$709.2211	$709.22	$709.25	$709.40