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	$137.87	12.461%	$155.05	$155.05	$155.05	$155.10
Purchase #2	$184.42	8.380%	$199.8744	$199.87	$199.85	$199.90
Purchase #3	$224.75	13.804%	$255.7745	$255.77	$255.75	$255.80
Purchase #4	$12.33	4.686%	$12.9078	$12.91	$12.90	$12.90
Purchase #5	$196.64	6.594%	$209.6064	$209.61	$209.60	$209.60
Purchase #6	$71.58	11.221%	$79.612	$79.61	$79.60	$79.60
Purchase #7	$165.83	12.456%	$186.4858	$186.49	$186.50	$186.50
7 purchase totals =	$993.42		$1,099.3109	$1,099.31	$1,099.25	$1,099.40