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	$210.54	13.243%	$238.4218	$238.42	$238.40	$238.40
Purchase #2	$103.89	5.341%	$109.4388	$109.44	$109.45	$109.40
Purchase #3	$57.45	12.811%	$64.8099	$64.81	$64.80	$64.80
Purchase #4	$189.33	6.316%	$201.2881	$201.29	$201.30	$201.30
Purchase #5	$113.63	7.821%	$122.517	$122.52	$122.50	$122.50
Purchase #6	$92.33	3.455%	$95.52	$95.52	$95.50	$95.50
Purchase #7	$145.25	4.275%	$151.4594	$151.46	$151.45	$151.50
7 purchase totals =	$912.42		$983.4550	$983.46	$983.40	$983.40