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	$107.72	5.576%	$113.7265	$113.73	$113.75	$113.70
Purchase #2	$106.45	4.404%	$111.1381	$111.14	$111.15	$111.10
Purchase #3	$12.43	3.756%	$12.8969	$12.90	$12.90	$12.90
Purchase #4	$180.80	8.862%	$196.8225	$196.82	$196.80	$196.80
Purchase #5	$14.88	10.451%	$16.4351	$16.44	$16.45	$16.40
Purchase #6	$134.54	4.166%	$140.1449	$140.14	$140.15	$140.10
Purchase #7	$73.32	3.130%	$75.6149	$75.61	$75.60	$75.60
7 purchase totals =	$630.14		$666.7789	$666.78	$666.80	$666.60