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	$73.67	6.248%	$78.2729	$78.27	$78.25	$78.30
Purchase #2	$50.64	13.467%	$57.4597	$57.46	$57.45	$57.50
Purchase #3	$32.85	7.461%	$35.3009	$35.30	$35.30	$35.30
Purchase #4	$13.70	11.283%	$15.2458	$15.25	$15.25	$15.20
Purchase #5	$244.88	3.400%	$253.2059	$253.21	$253.20	$253.20
Purchase #6	$13.76	12.138%	$15.4302	$15.43	$15.45	$15.40
Purchase #7	$148.78	11.234%	$165.4939	$165.49	$165.50	$165.50
7 purchase totals =	$578.28		$620.4093	$620.41	$620.40	$620.40