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	$129.70	12.276%	$145.622	$145.62	$145.60	$145.60
Purchase #2	$213.30	4.109%	$222.0645	$222.06	$222.05	$222.10
Purchase #3	$247.88	4.235%	$258.3777	$258.38	$258.40	$258.40
Purchase #4	$81.41	9.332%	$89.0072	$89.01	$89.00	$89.00
Purchase #5	$136.77	12.198%	$153.4532	$153.45	$153.45	$153.50
Purchase #6	$83.91	9.108%	$91.5525	$91.55	$91.55	$91.60
Purchase #7	$246.94	10.684%	$273.3231	$273.32	$273.30	$273.30
7 purchase totals =	$1,139.91		$1,233.4002	$1,233.39	$1,233.35	$1,233.50