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	$49.57	4.826%	$51.9622	$51.96	$51.95	$52.00
Purchase #2	$133.97	11.148%	$148.905	$148.91	$148.90	$148.90
Purchase #3	$24.92	13.504%	$28.2852	$28.29	$28.30	$28.30
Purchase #4	$39.68	10.470%	$43.8345	$43.83	$43.85	$43.80
Purchase #5	$41.45	9.341%	$45.3218	$45.32	$45.30	$45.30
Purchase #6	$139.59	3.834%	$144.9419	$144.94	$144.95	$144.90
Purchase #7	$179.85	13.592%	$204.2952	$204.30	$204.30	$204.30
7 purchase totals =	$609.03		$667.5458	$667.55	$667.55	$667.50