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	$42.34	7.464%	$45.5003	$45.50	$45.50	$45.50
Purchase #2	$189.61	6.692%	$202.2987	$202.30	$202.30	$202.30
Purchase #3	$160.31	3.131%	$165.3293	$165.33	$165.35	$165.30
Purchase #4	$230.25	3.402%	$238.0831	$238.08	$238.10	$238.10
Purchase #5	$134.53	13.738%	$153.0117	$153.01	$153.00	$153.00
Purchase #6	$102.91	9.693%	$112.8851	$112.89	$112.90	$112.90
Purchase #7	$34.70	13.639%	$39.4327	$39.43	$39.45	$39.40
7 purchase totals =	$894.65		$956.5409	$956.54	$956.60	$956.50