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	$91.87	8.849%	$99.9996	$100.00	$100.00	$100.00
Purchase #2	$56.45	4.604%	$59.049	$59.05	$59.05	$59.00
Purchase #3	$109.34	5.313%	$115.1492	$115.15	$115.15	$115.10
Purchase #4	$213.61	7.314%	$229.2334	$229.23	$229.25	$229.20
Purchase #5	$237.51	10.369%	$262.1374	$262.14	$262.15	$262.10
Purchase #6	$132.88	4.650%	$139.0589	$139.06	$139.05	$139.10
Purchase #7	$153.69	8.427%	$166.6415	$166.64	$166.65	$166.60
7 purchase totals =	$995.35		$1,071.2690	$1,071.27	$1,071.30	$1,071.10