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	$207.82	6.774%	$221.8977	$221.90	$221.90	$221.90
Purchase #2	$159.84	10.578%	$176.7479	$176.75	$176.75	$176.70
Purchase #3	$125.70	13.793%	$143.0378	$143.04	$143.05	$143.00
Purchase #4	$75.81	4.172%	$78.9728	$78.97	$78.95	$79.00
Purchase #5	$71.34	10.431%	$78.7815	$78.78	$78.80	$78.80
Purchase #6	$131.68	10.582%	$145.6144	$145.61	$145.60	$145.60
Purchase #7	$143.26	13.324%	$162.348	$162.35	$162.35	$162.30
7 purchase totals =	$915.45		$1,007.4001	$1,007.40	$1,007.40	$1,007.30