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	$120.37	8.698%	$130.8398	$130.84	$130.85	$130.80
Purchase #2	$61.87	5.780%	$65.4461	$65.45	$65.45	$65.40
Purchase #3	$213.57	6.365%	$227.1637	$227.16	$227.15	$227.20
Purchase #4	$101.89	9.824%	$111.8997	$111.90	$111.90	$111.90
Purchase #5	$219.87	10.679%	$243.3499	$243.35	$243.35	$243.30
Purchase #6	$66.45	12.428%	$74.7084	$74.71	$74.70	$74.70
Purchase #7	$106.94	10.397%	$118.0586	$118.06	$118.05	$118.10
7 purchase totals =	$890.96		$971.4662	$971.47	$971.45	$971.40