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	$159.40	8.137%	$172.3704	$172.37	$172.35	$172.40
Purchase #2	$138.77	9.173%	$151.4994	$151.50	$151.50	$151.50
Purchase #3	$124.61	9.834%	$136.8641	$136.86	$136.85	$136.90
Purchase #4	$129.78	9.368%	$141.9378	$141.94	$141.95	$141.90
Purchase #5	$117.52	11.816%	$131.4062	$131.41	$131.40	$131.40
Purchase #6	$131.95	13.268%	$149.4571	$149.46	$149.45	$149.50
Purchase #7	$21.45	4.517%	$22.4189	$22.42	$22.40	$22.40
7 purchase totals =	$823.48		$905.9539	$905.96	$905.90	$906.00