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	$152.42	13.268%	$172.6431	$172.64	$172.65	$172.60
Purchase #2	$97.33	7.425%	$104.5568	$104.56	$104.55	$104.60
Purchase #3	$130.78	6.744%	$139.5998	$139.60	$139.60	$139.60
Purchase #4	$102.62	8.471%	$111.3129	$111.31	$111.30	$111.30
Purchase #5	$236.95	4.581%	$247.8047	$247.80	$247.80	$247.80
Purchase #6	$22.80	6.470%	$24.2752	$24.28	$24.30	$24.30
Purchase #7	$118.31	8.810%	$128.7331	$128.73	$128.75	$128.70
7 purchase totals =	$861.21		$928.9256	$928.92	$928.95	$928.90