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	$103.59	13.199%	$117.2628	$117.26	$117.25	$117.30
Purchase #2	$43.82	4.719%	$45.8879	$45.89	$45.90	$45.90
Purchase #3	$151.74	4.847%	$159.0948	$159.09	$159.10	$159.10
Purchase #4	$44.27	3.530%	$45.8327	$45.83	$45.85	$45.80
Purchase #5	$69.91	12.256%	$78.4782	$78.48	$78.50	$78.50
Purchase #6	$31.52	9.277%	$34.4441	$34.44	$34.45	$34.40
Purchase #7	$141.27	6.481%	$150.4257	$150.43	$150.45	$150.40
7 purchase totals =	$586.12		$631.4262	$631.42	$631.50	$631.40