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	$30.98	3.394%	$32.0315	$32.03	$32.05	$32.00
Purchase #2	$151.39	10.410%	$167.1497	$167.15	$167.15	$167.10
Purchase #3	$241.38	4.711%	$252.7514	$252.75	$252.75	$252.80
Purchase #4	$229.39	11.672%	$256.1644	$256.16	$256.15	$256.20
Purchase #5	$162.45	6.699%	$173.3325	$173.33	$173.35	$173.30
Purchase #6	$63.25	7.330%	$67.8862	$67.89	$67.90	$67.90
Purchase #7	$123.58	4.275%	$128.863	$128.86	$128.85	$128.90
7 purchase totals =	$1,002.42		$1,078.1787	$1,078.17	$1,078.20	$1,078.20