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	$39.28	7.659%	$42.2885	$42.29	$42.30	$42.30
Purchase #2	$226.58	4.425%	$236.6062	$236.61	$236.60	$236.60
Purchase #3	$242.44	9.678%	$265.9033	$265.90	$265.90	$265.90
Purchase #4	$68.48	7.578%	$73.6694	$73.67	$73.65	$73.70
Purchase #5	$60.34	7.551%	$64.8963	$64.90	$64.90	$64.90
Purchase #6	$200.81	8.364%	$217.6057	$217.61	$217.60	$217.60
Purchase #7	$160.27	7.847%	$172.8464	$172.85	$172.85	$172.80
7 purchase totals =	$998.20		$1,073.8158	$1,073.83	$1,073.80	$1,073.80