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	$58.28	3.625%	$60.3927	$60.39	$60.40	$60.40
Purchase #2	$27.70	10.381%	$30.5755	$30.58	$30.60	$30.60
Purchase #3	$250.68	11.166%	$278.6709	$278.67	$278.65	$278.70
Purchase #4	$18.32	13.861%	$20.8593	$20.86	$20.85	$20.90
Purchase #5	$66.40	7.532%	$71.4012	$71.40	$71.40	$71.40
Purchase #6	$83.61	7.255%	$89.6759	$89.68	$89.70	$89.70
Purchase #7	$229.86	8.294%	$248.9246	$248.92	$248.90	$248.90
7 purchase totals =	$734.85		$800.5001	$800.50	$800.50	$800.60