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	$92.82	12.578%	$104.4949	$104.49	$104.50	$104.50
Purchase #2	$65.47	10.594%	$72.4059	$72.41	$72.40	$72.40
Purchase #3	$179.83	4.555%	$188.0213	$188.02	$188.00	$188.00
Purchase #4	$220.83	6.521%	$235.2303	$235.23	$235.25	$235.20
Purchase #5	$43.53	13.640%	$49.4675	$49.47	$49.45	$49.50
Purchase #6	$64.41	5.385%	$67.8785	$67.88	$67.90	$67.90
Purchase #7	$136.53	12.334%	$153.3696	$153.37	$153.35	$153.40
7 purchase totals =	$803.42		$870.8680	$870.87	$870.85	$870.90