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	$121.70	10.395%	$134.3507	$134.35	$134.35	$134.40
Purchase #2	$78.39	12.361%	$88.0798	$88.08	$88.10	$88.10
Purchase #3	$20.40	10.617%	$22.5659	$22.57	$22.55	$22.60
Purchase #4	$37.49	11.321%	$41.7342	$41.73	$41.75	$41.70
Purchase #5	$112.30	13.487%	$127.4459	$127.45	$127.45	$127.40
Purchase #6	$232.81	11.389%	$259.3247	$259.32	$259.30	$259.30
Purchase #7	$38.91	11.833%	$43.5142	$43.51	$43.50	$43.50
7 purchase totals =	$642.00		$717.0154	$717.01	$717.00	$717.00