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	$238.79	13.594%	$271.2511	$271.25	$271.25	$271.30
Purchase #2	$158.34	6.302%	$168.3186	$168.32	$168.30	$168.30
Purchase #3	$217.54	4.366%	$227.0378	$227.04	$227.05	$227.00
Purchase #4	$171.50	4.844%	$179.8075	$179.81	$179.80	$179.80
Purchase #5	$105.80	13.532%	$120.1169	$120.12	$120.10	$120.10
Purchase #6	$153.60	11.601%	$171.4191	$171.42	$171.40	$171.40
Purchase #7	$243.91	10.479%	$269.4693	$269.47	$269.45	$269.50
7 purchase totals =	$1,289.48		$1,407.4203	$1,407.43	$1,407.35	$1,407.40