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	$40.26	4.545%	$42.0898	$42.09	$42.10	$42.10
Purchase #2	$23.57	3.814%	$24.469	$24.47	$24.45	$24.50
Purchase #3	$104.84	4.779%	$109.8503	$109.85	$109.85	$109.90
Purchase #4	$144.54	4.383%	$150.8752	$150.88	$150.90	$150.90
Purchase #5	$40.96	4.778%	$42.9171	$42.92	$42.90	$42.90
Purchase #6	$60.29	3.798%	$62.5798	$62.58	$62.60	$62.60
Purchase #7	$53.86	11.632%	$60.125	$60.13	$60.15	$60.10
7 purchase totals =	$468.32		$492.9062	$492.92	$492.95	$493.00