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	$120.75	11.184%	$134.2547	$134.25	$134.25	$134.30
Purchase #2	$78.86	12.730%	$88.8989	$88.90	$88.90	$88.90
Purchase #3	$28.87	12.424%	$32.4568	$32.46	$32.45	$32.50
Purchase #4	$38.32	10.705%	$42.4222	$42.42	$42.40	$42.40
Purchase #5	$9.98	6.458%	$10.6245	$10.62	$10.60	$10.60
Purchase #6	$135.92	5.255%	$143.0626	$143.06	$143.05	$143.10
Purchase #7	$227.85	6.830%	$243.4122	$243.41	$243.40	$243.40
7 purchase totals =	$640.55		$695.1319	$695.12	$695.05	$695.20