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	$41.77	3.424%	$43.2002	$43.20	$43.20	$43.20
Purchase #2	$137.33	10.601%	$151.8884	$151.89	$151.90	$151.90
Purchase #3	$210.26	4.574%	$219.8773	$219.88	$219.90	$219.90
Purchase #4	$32.26	10.370%	$35.6054	$35.61	$35.60	$35.60
Purchase #5	$38.77	12.245%	$43.5174	$43.52	$43.50	$43.50
Purchase #6	$159.94	6.381%	$170.1458	$170.15	$170.15	$170.10
Purchase #7	$190.90	7.725%	$205.647	$205.65	$205.65	$205.60
7 purchase totals =	$811.23		$869.8815	$869.90	$869.90	$869.80