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	$29.61	5.242%	$31.1622	$31.16	$31.15	$31.20
Purchase #2	$35.61	4.735%	$37.2961	$37.30	$37.30	$37.30
Purchase #3	$101.91	9.680%	$111.7749	$111.77	$111.75	$111.80
Purchase #4	$94.43	10.665%	$104.501	$104.50	$104.50	$104.50
Purchase #5	$179.36	11.391%	$199.7909	$199.79	$199.80	$199.80
Purchase #6	$125.93	9.710%	$138.1578	$138.16	$138.15	$138.20
Purchase #7	$234.96	5.344%	$247.5163	$247.52	$247.50	$247.50
7 purchase totals =	$801.81		$870.1992	$870.20	$870.15	$870.30