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	$82.43	9.111%	$89.9402	$89.94	$89.95	$89.90
Purchase #2	$222.43	11.374%	$247.7292	$247.73	$247.75	$247.70
Purchase #3	$208.50	11.264%	$231.9854	$231.99	$232.00	$232.00
Purchase #4	$37.79	10.625%	$41.8052	$41.81	$41.80	$41.80
Purchase #5	$132.78	5.413%	$139.9674	$139.97	$139.95	$140.00
Purchase #6	$100.26	6.809%	$107.0867	$107.09	$107.10	$107.10
Purchase #7	$99.46	11.672%	$111.069	$111.07	$111.05	$111.10
7 purchase totals =	$883.65		$969.5831	$969.60	$969.60	$969.60