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	$52.93	9.872%	$58.1552	$58.16	$58.15	$58.20
Purchase #2	$84.31	3.392%	$87.1698	$87.17	$87.15	$87.20
Purchase #3	$16.69	11.402%	$18.593	$18.59	$18.60	$18.60
Purchase #4	$235.84	10.788%	$261.2824	$261.28	$261.30	$261.30
Purchase #5	$49.69	9.716%	$54.5179	$54.52	$54.50	$54.50
Purchase #6	$66.51	7.320%	$71.3785	$71.38	$71.40	$71.40
Purchase #7	$105.90	3.599%	$109.7113	$109.71	$109.70	$109.70
7 purchase totals =	$611.87		$660.8081	$660.81	$660.80	$660.90