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	$18.49	12.379%	$20.7789	$20.78	$20.80	$20.80
Purchase #2	$121.36	5.527%	$128.0676	$128.07	$128.05	$128.10
Purchase #3	$238.77	10.315%	$263.3991	$263.40	$263.40	$263.40
Purchase #4	$140.51	13.656%	$159.698	$159.70	$159.70	$159.70
Purchase #5	$125.49	11.289%	$139.6566	$139.66	$139.65	$139.70
Purchase #6	$126.62	12.264%	$142.1487	$142.15	$142.15	$142.10
Purchase #7	$143.37	6.103%	$152.1199	$152.12	$152.10	$152.10
7 purchase totals =	$914.61		$1,005.8688	$1,005.88	$1,005.85	$1,005.90