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	$79.84	12.670%	$89.9557	$89.96	$89.95	$90.00
Purchase #2	$86.93	6.124%	$92.2536	$92.25	$92.25	$92.30
Purchase #3	$9.72	6.855%	$10.3863	$10.39	$10.40	$10.40
Purchase #4	$134.50	12.756%	$151.6568	$151.66	$151.65	$151.70
Purchase #5	$35.58	7.567%	$38.2723	$38.27	$38.25	$38.30
Purchase #6	$204.27	6.335%	$217.2105	$217.21	$217.20	$217.20
Purchase #7	$102.54	10.104%	$112.9006	$112.90	$112.90	$112.90
7 purchase totals =	$653.38		$712.6358	$712.64	$712.60	$712.80