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	$157.62	6.452%	$167.7896	$167.79	$167.80	$167.80
Purchase #2	$37.25	9.507%	$40.7914	$40.79	$40.80	$40.80
Purchase #3	$79.44	3.874%	$82.5175	$82.52	$82.50	$82.50
Purchase #4	$10.76	3.762%	$11.1648	$11.16	$11.15	$11.20
Purchase #5	$58.79	4.572%	$61.4779	$61.48	$61.50	$61.50
Purchase #6	$92.89	13.750%	$105.6624	$105.66	$105.65	$105.70
Purchase #7	$176.75	11.745%	$197.5093	$197.51	$197.50	$197.50
7 purchase totals =	$613.50		$666.9129	$666.91	$666.90	$667.00