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	$89.76	11.168%	$99.7844	$99.78	$99.80	$99.80
Purchase #2	$82.83	4.800%	$86.8058	$86.81	$86.80	$86.80
Purchase #3	$127.51	12.461%	$143.399	$143.40	$143.40	$143.40
Purchase #4	$43.68	11.151%	$48.5508	$48.55	$48.55	$48.60
Purchase #5	$74.82	3.418%	$77.3773	$77.38	$77.40	$77.40
Purchase #6	$202.71	6.727%	$216.3463	$216.35	$216.35	$216.30
Purchase #7	$65.95	4.858%	$69.1539	$69.15	$69.15	$69.20
7 purchase totals =	$687.26		$741.4175	$741.42	$741.45	$741.50