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	$17.38	4.552%	$18.1711	$18.17	$18.15	$18.20
Purchase #2	$54.94	5.340%	$57.8738	$57.87	$57.85	$57.90
Purchase #3	$24.97	3.462%	$25.8345	$25.83	$25.85	$25.80
Purchase #4	$82.42	11.408%	$91.8225	$91.82	$91.80	$91.80
Purchase #5	$171.68	11.531%	$191.4764	$191.48	$191.50	$191.50
Purchase #6	$143.59	10.460%	$158.6095	$158.61	$158.60	$158.60
Purchase #7	$224.55	12.816%	$253.3283	$253.33	$253.35	$253.30
7 purchase totals =	$719.53		$797.1161	$797.11	$797.10	$797.10