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	$113.58	11.619%	$126.7769	$126.78	$126.80	$126.80
Purchase #2	$49.95	4.809%	$52.3521	$52.35	$52.35	$52.40
Purchase #3	$234.90	6.522%	$250.2202	$250.22	$250.20	$250.20
Purchase #4	$231.46	9.231%	$252.8261	$252.83	$252.85	$252.80
Purchase #5	$24.74	11.218%	$27.5153	$27.52	$27.50	$27.50
Purchase #6	$87.92	13.208%	$99.5325	$99.53	$99.55	$99.50
Purchase #7	$201.85	4.272%	$210.473	$210.47	$210.45	$210.50
7 purchase totals =	$944.40		$1,019.6961	$1,019.70	$1,019.70	$1,019.70