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	$33.96	9.577%	$37.2123	$37.21	$37.20	$37.20
Purchase #2	$247.77	10.780%	$274.4796	$274.48	$274.50	$274.50
Purchase #3	$136.52	8.670%	$148.3563	$148.36	$148.35	$148.40
Purchase #4	$106.86	9.146%	$116.6334	$116.63	$116.65	$116.60
Purchase #5	$130.37	5.832%	$137.9732	$137.97	$137.95	$138.00
Purchase #6	$156.74	9.823%	$172.1366	$172.14	$172.15	$172.10
Purchase #7	$121.50	4.616%	$127.1084	$127.11	$127.10	$127.10
7 purchase totals =	$933.72		$1,013.8998	$1,013.90	$1,013.90	$1,013.90