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	$94.36	11.569%	$105.2765	$105.28	$105.30	$105.30
Purchase #2	$42.83	12.722%	$48.2788	$48.28	$48.30	$48.30
Purchase #3	$237.42	8.241%	$256.9858	$256.99	$257.00	$257.00
Purchase #4	$101.32	8.294%	$109.7235	$109.72	$109.70	$109.70
Purchase #5	$47.97	13.108%	$54.2579	$54.26	$54.25	$54.30
Purchase #6	$130.25	9.598%	$142.7514	$142.75	$142.75	$142.80
Purchase #7	$192.89	3.596%	$199.8263	$199.83	$199.85	$199.80
7 purchase totals =	$847.04		$917.1002	$917.11	$917.15	$917.20