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	$133.62	11.736%	$149.3016	$149.30	$149.30	$149.30
Purchase #2	$241.31	9.688%	$264.6881	$264.69	$264.70	$264.70
Purchase #3	$144.47	4.624%	$151.1503	$151.15	$151.15	$151.20
Purchase #4	$153.30	9.863%	$168.42	$168.42	$168.40	$168.40
Purchase #5	$104.64	11.557%	$116.7332	$116.73	$116.75	$116.70
Purchase #6	$83.38	13.316%	$94.4829	$94.48	$94.50	$94.50
Purchase #7	$10.46	3.543%	$10.8306	$10.83	$10.85	$10.80
7 purchase totals =	$871.18		$955.6067	$955.60	$955.65	$955.60