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	$230.83	9.116%	$251.8725	$251.87	$251.85	$251.90
Purchase #2	$149.56	6.802%	$159.7331	$159.73	$159.75	$159.70
Purchase #3	$209.91	11.825%	$234.7319	$234.73	$234.75	$234.70
Purchase #4	$108.47	5.128%	$114.0323	$114.03	$114.05	$114.00
Purchase #5	$238.47	7.160%	$255.5445	$255.54	$255.55	$255.50
Purchase #6	$212.68	13.604%	$241.613	$241.61	$241.60	$241.60
Purchase #7	$38.86	11.243%	$43.229	$43.23	$43.25	$43.20
7 purchase totals =	$1,188.78		$1,300.7563	$1,300.74	$1,300.80	$1,300.60