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	$110.60	11.566%	$123.392	$123.39	$123.40	$123.40
Purchase #2	$198.49	7.740%	$213.8531	$213.85	$213.85	$213.90
Purchase #3	$134.84	6.349%	$143.401	$143.40	$143.40	$143.40
Purchase #4	$43.99	13.547%	$49.9493	$49.95	$49.95	$49.90
Purchase #5	$125.32	4.103%	$130.4619	$130.46	$130.45	$130.50
Purchase #6	$118.89	11.241%	$132.2544	$132.25	$132.25	$132.30
Purchase #7	$5.89	4.523%	$6.1564	$6.16	$6.15	$6.20
7 purchase totals =	$738.02		$799.4681	$799.46	$799.45	$799.60