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	$106.90	4.674%	$111.8965	$111.90	$111.90	$111.90
Purchase #2	$190.64	10.588%	$210.825	$210.83	$210.85	$210.80
Purchase #3	$168.72	4.749%	$176.7325	$176.73	$176.75	$176.70
Purchase #4	$114.33	6.532%	$121.798	$121.80	$121.80	$121.80
Purchase #5	$148.97	10.732%	$164.9575	$164.96	$164.95	$165.00
Purchase #6	$146.39	10.404%	$161.6204	$161.62	$161.60	$161.60
Purchase #7	$145.57	4.127%	$151.5777	$151.58	$151.60	$151.60
7 purchase totals =	$1,021.52		$1,099.4076	$1,099.42	$1,099.45	$1,099.40