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	$136.64	5.663%	$144.3779	$144.38	$144.40	$144.40
Purchase #2	$183.89	13.546%	$208.7997	$208.80	$208.80	$208.80
Purchase #3	$59.66	6.604%	$63.5999	$63.60	$63.60	$63.60
Purchase #4	$48.28	11.162%	$53.669	$53.67	$53.65	$53.70
Purchase #5	$163.25	13.523%	$185.3263	$185.33	$185.35	$185.30
Purchase #6	$42.35	6.619%	$45.1531	$45.15	$45.15	$45.20
Purchase #7	$147.44	8.454%	$159.9046	$159.90	$159.90	$159.90
7 purchase totals =	$781.51		$860.8305	$860.83	$860.85	$860.90