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	$20.33	8.457%	$22.0493	$22.05	$22.05	$22.00
Purchase #2	$18.88	5.496%	$19.9176	$19.92	$19.90	$19.90
Purchase #3	$140.79	3.210%	$145.3094	$145.31	$145.30	$145.30
Purchase #4	$176.44	13.546%	$200.3406	$200.34	$200.35	$200.30
Purchase #5	$152.61	4.788%	$159.917	$159.92	$159.90	$159.90
Purchase #6	$92.93	11.110%	$103.2545	$103.25	$103.25	$103.30
Purchase #7	$27.85	3.698%	$28.8799	$28.88	$28.90	$28.90
7 purchase totals =	$629.83		$679.6683	$679.67	$679.65	$679.60