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	$22.69	12.475%	$25.5206	$25.52	$25.50	$25.50
Purchase #2	$114.56	4.189%	$119.3589	$119.36	$119.35	$119.40
Purchase #3	$188.83	11.472%	$210.4926	$210.49	$210.50	$210.50
Purchase #4	$45.59	6.418%	$48.516	$48.52	$48.50	$48.50
Purchase #5	$28.74	12.434%	$32.3135	$32.31	$32.30	$32.30
Purchase #6	$32.78	3.118%	$33.8021	$33.80	$33.80	$33.80
Purchase #7	$9.30	12.733%	$10.4842	$10.48	$10.50	$10.50
7 purchase totals =	$442.49		$480.4879	$480.48	$480.45	$480.50