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	$122.59	3.273%	$126.6024	$126.60	$126.60	$126.60
Purchase #2	$166.49	8.766%	$181.0845	$181.08	$181.10	$181.10
Purchase #3	$152.27	13.137%	$172.2737	$172.27	$172.25	$172.30
Purchase #4	$83.26	9.309%	$91.0107	$91.01	$91.00	$91.00
Purchase #5	$225.72	9.159%	$246.3937	$246.39	$246.40	$246.40
Purchase #6	$179.28	6.112%	$190.2376	$190.24	$190.25	$190.20
Purchase #7	$244.81	7.142%	$262.2943	$262.29	$262.30	$262.30
7 purchase totals =	$1,174.42		$1,269.8969	$1,269.88	$1,269.90	$1,269.90