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	$166.50	9.180%	$181.7847	$181.78	$181.80	$181.80
Purchase #2	$211.64	4.552%	$221.2739	$221.27	$221.25	$221.30
Purchase #3	$182.86	8.559%	$198.511	$198.51	$198.50	$198.50
Purchase #4	$116.31	6.146%	$123.4584	$123.46	$123.45	$123.50
Purchase #5	$243.82	3.528%	$252.422	$252.42	$252.40	$252.40
Purchase #6	$91.65	5.740%	$96.9107	$96.91	$96.90	$96.90
Purchase #7	$130.29	12.489%	$146.5619	$146.56	$146.55	$146.60
7 purchase totals =	$1,143.07		$1,220.9226	$1,220.91	$1,220.85	$1,221.00