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	$234.49	12.594%	$264.0217	$264.02	$264.00	$264.00
Purchase #2	$53.37	7.429%	$57.3349	$57.33	$57.35	$57.30
Purchase #3	$219.66	5.810%	$232.4222	$232.42	$232.40	$232.40
Purchase #4	$69.68	3.516%	$72.1299	$72.13	$72.15	$72.10
Purchase #5	$22.75	13.826%	$25.8954	$25.90	$25.90	$25.90
Purchase #6	$123.53	3.303%	$127.6102	$127.61	$127.60	$127.60
Purchase #7	$153.52	3.543%	$158.9592	$158.96	$158.95	$159.00
7 purchase totals =	$877.00		$938.3735	$938.37	$938.35	$938.30