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	$160.90	5.464%	$169.6916	$169.69	$169.70	$169.70
Purchase #2	$248.48	8.734%	$270.1822	$270.18	$270.20	$270.20
Purchase #3	$101.62	4.187%	$105.8748	$105.87	$105.85	$105.90
Purchase #4	$123.49	3.660%	$128.0097	$128.01	$128.00	$128.00
Purchase #5	$80.33	11.468%	$89.5422	$89.54	$89.55	$89.50
Purchase #6	$48.91	3.547%	$50.6448	$50.64	$50.65	$50.60
Purchase #7	$9.82	13.662%	$11.1616	$11.16	$11.15	$11.20
7 purchase totals =	$773.55		$825.1069	$825.09	$825.10	$825.10