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	$97.82	6.201%	$103.8858	$103.89	$103.90	$103.90
Purchase #2	$196.88	12.194%	$220.8875	$220.89	$220.90	$220.90
Purchase #3	$169.35	11.221%	$188.3528	$188.35	$188.35	$188.40
Purchase #4	$143.86	11.303%	$160.1205	$160.12	$160.10	$160.10
Purchase #5	$185.81	12.802%	$209.5974	$209.60	$209.60	$209.60
Purchase #6	$187.32	4.600%	$195.9367	$195.94	$195.95	$195.90
Purchase #7	$246.86	5.522%	$260.4916	$260.49	$260.50	$260.50
7 purchase totals =	$1,227.90		$1,339.2723	$1,339.28	$1,339.30	$1,339.30