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	$172.93	10.325%	$190.785	$190.79	$190.80	$190.80
Purchase #2	$121.96	5.712%	$128.9264	$128.93	$128.95	$128.90
Purchase #3	$126.56	4.105%	$131.7553	$131.76	$131.75	$131.80
Purchase #4	$81.72	10.346%	$90.1748	$90.17	$90.15	$90.20
Purchase #5	$50.99	13.591%	$57.9201	$57.92	$57.90	$57.90
Purchase #6	$205.69	11.791%	$229.9429	$229.94	$229.95	$229.90
Purchase #7	$117.43	5.666%	$124.0836	$124.08	$124.10	$124.10
7 purchase totals =	$877.28		$953.5881	$953.59	$953.60	$953.60