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	$131.91	13.774%	$150.0793	$150.08	$150.10	$150.10
Purchase #2	$61.70	6.747%	$65.8629	$65.86	$65.85	$65.90
Purchase #3	$115.60	13.114%	$130.7598	$130.76	$130.75	$130.80
Purchase #4	$135.32	4.470%	$141.3688	$141.37	$141.35	$141.40
Purchase #5	$173.54	5.174%	$182.519	$182.52	$182.50	$182.50
Purchase #6	$137.86	11.616%	$153.8738	$153.87	$153.85	$153.90
Purchase #7	$231.79	6.390%	$246.6014	$246.60	$246.60	$246.60
7 purchase totals =	$987.72		$1,071.0650	$1,071.06	$1,071.00	$1,071.20