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	$50.78	5.371%	$53.5074	$53.51	$53.50	$53.50
Purchase #2	$172.32	9.870%	$189.328	$189.33	$189.35	$189.30
Purchase #3	$106.94	11.540%	$119.2809	$119.28	$119.30	$119.30
Purchase #4	$55.90	4.803%	$58.5849	$58.58	$58.60	$58.60
Purchase #5	$136.52	9.446%	$149.4157	$149.42	$149.40	$149.40
Purchase #6	$221.73	3.118%	$228.6435	$228.64	$228.65	$228.60
Purchase #7	$99.79	11.663%	$111.4285	$111.43	$111.45	$111.40
7 purchase totals =	$843.98		$910.1889	$910.19	$910.25	$910.10