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	$208.86	4.299%	$217.8389	$217.84	$217.85	$217.80
Purchase #2	$100.40	12.788%	$113.2392	$113.24	$113.25	$113.20
Purchase #3	$141.81	3.827%	$147.2371	$147.24	$147.25	$147.20
Purchase #4	$11.61	6.230%	$12.3333	$12.33	$12.35	$12.30
Purchase #5	$99.50	12.158%	$111.5972	$111.60	$111.60	$111.60
Purchase #6	$162.63	6.533%	$173.2546	$173.25	$173.25	$173.30
Purchase #7	$23.46	5.163%	$24.6712	$24.67	$24.65	$24.70
7 purchase totals =	$748.27		$800.1715	$800.17	$800.20	$800.10