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	$160.74	11.426%	$179.1062	$179.11	$179.10	$179.10
Purchase #2	$191.56	9.802%	$210.3367	$210.34	$210.35	$210.30
Purchase #3	$103.60	4.212%	$107.9636	$107.96	$107.95	$108.00
Purchase #4	$145.78	8.168%	$157.6873	$157.69	$157.70	$157.70
Purchase #5	$165.45	11.404%	$184.3179	$184.32	$184.30	$184.30
Purchase #6	$52.72	13.388%	$59.7782	$59.78	$59.80	$59.80
Purchase #7	$20.29	3.787%	$21.0584	$21.06	$21.05	$21.10
7 purchase totals =	$840.14		$920.2483	$920.26	$920.25	$920.30