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	$156.64	6.141%	$166.2593	$166.26	$166.25	$166.30
Purchase #2	$91.91	4.723%	$96.2509	$96.25	$96.25	$96.30
Purchase #3	$37.56	8.723%	$40.8364	$40.84	$40.85	$40.80
Purchase #4	$20.86	13.200%	$23.6135	$23.61	$23.60	$23.60
Purchase #5	$74.80	10.827%	$82.8986	$82.90	$82.90	$82.90
Purchase #6	$49.86	11.144%	$55.4164	$55.42	$55.40	$55.40
Purchase #7	$64.95	12.461%	$73.0434	$73.04	$73.05	$73.00
7 purchase totals =	$496.58		$538.3185	$538.32	$538.30	$538.30