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	$92.34	7.352%	$99.1288	$99.13	$99.15	$99.10
Purchase #2	$110.96	6.837%	$118.5463	$118.55	$118.55	$118.50
Purchase #3	$227.80	12.183%	$255.5529	$255.55	$255.55	$255.60
Purchase #4	$112.45	13.624%	$127.7702	$127.77	$127.75	$127.80
Purchase #5	$180.51	5.448%	$190.3442	$190.34	$190.35	$190.30
Purchase #6	$134.54	6.422%	$143.1802	$143.18	$143.20	$143.20
Purchase #7	$88.98	8.832%	$96.8387	$96.84	$96.85	$96.80
7 purchase totals =	$947.58		$1,031.3613	$1,031.36	$1,031.40	$1,031.30