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	$54.83	10.363%	$60.512	$60.51	$60.50	$60.50
Purchase #2	$18.46	13.294%	$20.9141	$20.91	$20.90	$20.90
Purchase #3	$115.25	3.198%	$118.9357	$118.94	$118.95	$118.90
Purchase #4	$116.96	12.791%	$131.9204	$131.92	$131.90	$131.90
Purchase #5	$55.94	7.508%	$60.14	$60.14	$60.15	$60.10
Purchase #6	$175.68	13.580%	$199.5373	$199.54	$199.55	$199.50
Purchase #7	$50.67	3.614%	$52.5012	$52.50	$52.50	$52.50
7 purchase totals =	$587.79		$644.4607	$644.46	$644.45	$644.30