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	$40.89	8.709%	$44.4511	$44.45	$44.45	$44.50
Purchase #2	$220.52	5.726%	$233.147	$233.15	$233.15	$233.10
Purchase #3	$27.43	13.420%	$31.1111	$31.11	$31.10	$31.10
Purchase #4	$171.28	8.522%	$185.8765	$185.88	$185.90	$185.90
Purchase #5	$129.89	13.568%	$147.5135	$147.51	$147.50	$147.50
Purchase #6	$214.83	13.516%	$243.8664	$243.87	$243.85	$243.90
Purchase #7	$213.46	7.828%	$230.1696	$230.17	$230.15	$230.20
7 purchase totals =	$1,018.30		$1,116.1352	$1,116.14	$1,116.10	$1,116.20