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	$64.92	11.828%	$72.5987	$72.60	$72.60	$72.60
Purchase #2	$55.43	12.514%	$62.3665	$62.37	$62.35	$62.40
Purchase #3	$10.30	4.276%	$10.7404	$10.74	$10.75	$10.70
Purchase #4	$201.46	4.353%	$210.2296	$210.23	$210.25	$210.20
Purchase #5	$11.51	12.134%	$12.9066	$12.91	$12.90	$12.90
Purchase #6	$82.67	12.616%	$93.0996	$93.10	$93.10	$93.10
Purchase #7	$174.45	8.289%	$188.9102	$188.91	$188.90	$188.90
7 purchase totals =	$600.74		$650.8516	$650.86	$650.85	$650.80