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	$143.51	12.694%	$161.7272	$161.73	$161.75	$161.70
Purchase #2	$172.37	7.108%	$184.6221	$184.62	$184.60	$184.60
Purchase #3	$101.97	7.172%	$109.2833	$109.28	$109.30	$109.30
Purchase #4	$90.30	9.408%	$98.7954	$98.80	$98.80	$98.80
Purchase #5	$18.75	8.102%	$20.2691	$20.27	$20.25	$20.30
Purchase #6	$97.60	12.385%	$109.6878	$109.69	$109.70	$109.70
Purchase #7	$139.60	10.233%	$153.8853	$153.89	$153.90	$153.90
7 purchase totals =	$764.10		$838.2702	$838.28	$838.30	$838.30