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	$115.36	11.389%	$128.4984	$128.50	$128.50	$128.50
Purchase #2	$77.27	4.690%	$80.894	$80.89	$80.90	$80.90
Purchase #3	$162.90	5.716%	$172.2114	$172.21	$172.20	$172.20
Purchase #4	$26.36	11.757%	$29.4591	$29.46	$29.45	$29.50
Purchase #5	$203.64	7.620%	$219.1574	$219.16	$219.15	$219.20
Purchase #6	$127.73	12.583%	$143.8023	$143.80	$143.80	$143.80
Purchase #7	$229.89	11.473%	$256.2653	$256.27	$256.25	$256.30
7 purchase totals =	$943.15		$1,030.2879	$1,030.29	$1,030.25	$1,030.40