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	$27.64	3.514%	$28.6113	$28.61	$28.60	$28.60
Purchase #2	$33.93	11.679%	$37.8927	$37.89	$37.90	$37.90
Purchase #3	$40.45	11.179%	$44.9719	$44.97	$44.95	$45.00
Purchase #4	$89.83	5.617%	$94.8758	$94.88	$94.90	$94.90
Purchase #5	$119.63	10.160%	$131.7844	$131.78	$131.80	$131.80
Purchase #6	$24.61	4.346%	$25.6796	$25.68	$25.70	$25.70
Purchase #7	$138.38	12.221%	$155.2914	$155.29	$155.30	$155.30
7 purchase totals =	$474.47		$519.1071	$519.10	$519.15	$519.20