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	$72.87	7.261%	$78.1611	$78.16	$78.15	$78.20
Purchase #2	$58.36	5.823%	$61.7583	$61.76	$61.75	$61.80
Purchase #3	$32.41	9.561%	$35.5087	$35.51	$35.50	$35.50
Purchase #4	$62.92	13.346%	$71.3173	$71.32	$71.30	$71.30
Purchase #5	$43.26	10.594%	$47.843	$47.84	$47.85	$47.80
Purchase #6	$56.53	9.268%	$61.7692	$61.77	$61.75	$61.80
Purchase #7	$232.45	8.364%	$251.8921	$251.89	$251.90	$251.90
7 purchase totals =	$558.80		$608.2497	$608.25	$608.20	$608.30