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	$55.77	13.468%	$63.2811	$63.28	$63.30	$63.30
Purchase #2	$28.89	12.264%	$32.4331	$32.43	$32.45	$32.40
Purchase #3	$224.99	8.388%	$243.8622	$243.86	$243.85	$243.90
Purchase #4	$173.84	9.566%	$190.4695	$190.47	$190.45	$190.50
Purchase #5	$155.73	11.758%	$174.0407	$174.04	$174.05	$174.00
Purchase #6	$101.51	12.130%	$113.8232	$113.82	$113.80	$113.80
Purchase #7	$210.30	10.758%	$232.9241	$232.92	$232.90	$232.90
7 purchase totals =	$951.03		$1,050.8339	$1,050.82	$1,050.80	$1,050.80