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	$87.28	13.628%	$99.1745	$99.17	$99.15	$99.20
Purchase #2	$174.96	10.147%	$192.7132	$192.71	$192.70	$192.70
Purchase #3	$7.73	9.572%	$8.4699	$8.47	$8.45	$8.50
Purchase #4	$54.57	6.161%	$57.9321	$57.93	$57.95	$57.90
Purchase #5	$98.59	4.483%	$103.0098	$103.01	$103.00	$103.00
Purchase #6	$32.92	13.531%	$37.3744	$37.37	$37.35	$37.40
Purchase #7	$108.68	7.641%	$116.9842	$116.98	$117.00	$117.00
7 purchase totals =	$564.73		$615.6581	$615.64	$615.60	$615.70