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	$199.55	11.705%	$222.9073	$222.91	$222.90	$222.90
Purchase #2	$148.72	5.212%	$156.4713	$156.47	$156.45	$156.50
Purchase #3	$15.92	5.634%	$16.8169	$16.82	$16.80	$16.80
Purchase #4	$141.72	9.380%	$155.0133	$155.01	$155.00	$155.00
Purchase #5	$139.51	11.531%	$155.5969	$155.60	$155.60	$155.60
Purchase #6	$61.67	9.792%	$67.7087	$67.71	$67.70	$67.70
Purchase #7	$127.73	7.671%	$137.5282	$137.53	$137.55	$137.50
7 purchase totals =	$834.82		$912.0426	$912.05	$912.00	$912.00