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	$21.36	4.132%	$22.2426	$22.24	$22.25	$22.20
Purchase #2	$158.46	3.836%	$164.5385	$164.54	$164.55	$164.50
Purchase #3	$110.36	8.316%	$119.5375	$119.54	$119.55	$119.50
Purchase #4	$77.43	7.408%	$83.166	$83.17	$83.15	$83.20
Purchase #5	$156.72	5.685%	$165.6295	$165.63	$165.65	$165.60
Purchase #6	$91.40	8.109%	$98.8116	$98.81	$98.80	$98.80
Purchase #7	$23.51	4.567%	$24.5837	$24.58	$24.60	$24.60
7 purchase totals =	$639.24		$678.5094	$678.51	$678.55	$678.40