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	$142.54	12.293%	$160.0624	$160.06	$160.05	$160.10
Purchase #2	$15.91	11.691%	$17.77	$17.77	$17.75	$17.80
Purchase #3	$242.29	10.659%	$268.1157	$268.12	$268.10	$268.10
Purchase #4	$191.52	7.810%	$206.4777	$206.48	$206.50	$206.50
Purchase #5	$142.96	11.104%	$158.8343	$158.83	$158.85	$158.80
Purchase #6	$26.82	10.435%	$29.6187	$29.62	$29.60	$29.60
Purchase #7	$54.50	8.767%	$59.278	$59.28	$59.30	$59.30
7 purchase totals =	$816.54		$900.1568	$900.16	$900.15	$900.20