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	$52.59	12.591%	$59.2116	$59.21	$59.20	$59.20
Purchase #2	$10.80	6.473%	$11.4991	$11.50	$11.50	$11.50
Purchase #3	$49.76	9.184%	$54.33	$54.33	$54.35	$54.30
Purchase #4	$50.43	10.210%	$55.5789	$55.58	$55.60	$55.60
Purchase #5	$209.95	10.525%	$232.0472	$232.05	$232.05	$232.00
Purchase #6	$250.78	11.590%	$279.8454	$279.85	$279.85	$279.80
Purchase #7	$143.97	4.139%	$149.9289	$149.93	$149.95	$149.90
7 purchase totals =	$768.28		$842.4411	$842.45	$842.50	$842.30