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	$159.39	6.196%	$169.2658	$169.27	$169.25	$169.30
Purchase #2	$150.87	13.344%	$171.0021	$171.00	$171.00	$171.00
Purchase #3	$91.68	9.719%	$100.5904	$100.59	$100.60	$100.60
Purchase #4	$21.89	7.425%	$23.5153	$23.52	$23.50	$23.50
Purchase #5	$132.38	7.362%	$142.1258	$142.13	$142.15	$142.10
Purchase #6	$132.31	9.843%	$145.3333	$145.33	$145.35	$145.30
Purchase #7	$113.72	3.279%	$117.4489	$117.45	$117.45	$117.40
7 purchase totals =	$802.24		$869.2816	$869.29	$869.30	$869.20