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	$143.82	12.729%	$162.1268	$162.13	$162.15	$162.10
Purchase #2	$53.70	11.356%	$59.7982	$59.80	$59.80	$59.80
Purchase #3	$211.35	3.734%	$219.2418	$219.24	$219.25	$219.20
Purchase #4	$35.56	7.522%	$38.2348	$38.23	$38.25	$38.20
Purchase #5	$90.29	10.453%	$99.728	$99.73	$99.75	$99.70
Purchase #6	$63.29	10.189%	$69.7386	$69.74	$69.75	$69.70
Purchase #7	$34.50	8.468%	$37.4215	$37.42	$37.40	$37.40
7 purchase totals =	$632.51		$686.2897	$686.29	$686.35	$686.10