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	$124.57	11.438%	$138.8183	$138.82	$138.80	$138.80
Purchase #2	$52.65	12.777%	$59.3771	$59.38	$59.40	$59.40
Purchase #3	$83.34	5.331%	$87.7829	$87.78	$87.80	$87.80
Purchase #4	$18.58	5.555%	$19.6121	$19.61	$19.60	$19.60
Purchase #5	$59.29	11.665%	$66.2062	$66.21	$66.20	$66.20
Purchase #6	$239.94	10.125%	$264.2339	$264.23	$264.25	$264.20
Purchase #7	$216.91	8.119%	$234.5209	$234.52	$234.50	$234.50
7 purchase totals =	$795.28		$870.5514	$870.55	$870.55	$870.50