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	$229.84	3.801%	$238.5762	$238.58	$238.60	$238.60
Purchase #2	$210.90	3.306%	$217.8724	$217.87	$217.85	$217.90
Purchase #3	$120.48	10.268%	$132.8509	$132.85	$132.85	$132.90
Purchase #4	$49.80	7.513%	$53.5415	$53.54	$53.55	$53.50
Purchase #5	$221.75	11.719%	$247.7369	$247.74	$247.75	$247.70
Purchase #6	$127.60	3.229%	$131.7202	$131.72	$131.70	$131.70
Purchase #7	$121.99	4.740%	$127.7723	$127.77	$127.75	$127.80
7 purchase totals =	$1,082.36		$1,150.0704	$1,150.07	$1,150.05	$1,150.10