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	$206.33	11.444%	$229.9424	$229.94	$229.95	$229.90
Purchase #2	$115.38	7.398%	$123.9158	$123.92	$123.90	$123.90
Purchase #3	$87.77	3.556%	$90.8911	$90.89	$90.90	$90.90
Purchase #4	$13.56	4.148%	$14.1225	$14.12	$14.10	$14.10
Purchase #5	$203.25	9.578%	$222.7173	$222.72	$222.70	$222.70
Purchase #6	$11.80	8.416%	$12.7931	$12.79	$12.80	$12.80
Purchase #7	$17.37	6.515%	$18.5017	$18.50	$18.50	$18.50
7 purchase totals =	$655.46		$712.8839	$712.88	$712.85	$712.80