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	$39.85	7.786%	$42.9527	$42.95	$42.95	$43.00
Purchase #2	$231.87	12.856%	$261.6792	$261.68	$261.70	$261.70
Purchase #3	$50.96	13.693%	$57.938	$57.94	$57.95	$57.90
Purchase #4	$139.87	5.434%	$147.4705	$147.47	$147.45	$147.50
Purchase #5	$60.28	8.856%	$65.6184	$65.62	$65.60	$65.60
Purchase #6	$5.61	10.723%	$6.2116	$6.21	$6.20	$6.20
Purchase #7	$79.27	12.607%	$89.2636	$89.26	$89.25	$89.30
7 purchase totals =	$607.71		$671.1340	$671.13	$671.10	$671.20