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	$113.87	12.671%	$128.2985	$128.30	$128.30	$128.30
Purchase #2	$99.93	4.521%	$104.4478	$104.45	$104.45	$104.40
Purchase #3	$95.38	10.229%	$105.1364	$105.14	$105.15	$105.10
Purchase #4	$23.56	4.691%	$24.6652	$24.67	$24.65	$24.70
Purchase #5	$179.35	11.654%	$200.2514	$200.25	$200.25	$200.30
Purchase #6	$31.51	12.417%	$35.4226	$35.42	$35.40	$35.40
Purchase #7	$137.59	8.321%	$149.0389	$149.04	$149.05	$149.00
7 purchase totals =	$681.19		$747.2608	$747.27	$747.25	$747.20