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	$21.35	7.354%	$22.9201	$22.92	$22.90	$22.90
Purchase #2	$134.59	13.105%	$152.228	$152.23	$152.25	$152.20
Purchase #3	$16.76	4.142%	$17.4542	$17.45	$17.45	$17.50
Purchase #4	$89.69	3.605%	$92.9233	$92.92	$92.90	$92.90
Purchase #5	$25.81	6.574%	$27.5067	$27.51	$27.50	$27.50
Purchase #6	$80.54	3.660%	$83.4878	$83.49	$83.50	$83.50
Purchase #7	$107.44	6.712%	$114.6514	$114.65	$114.65	$114.70
7 purchase totals =	$476.18		$511.1715	$511.17	$511.15	$511.20