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	$57.73	12.225%	$64.7875	$64.79	$64.80	$64.80
Purchase #2	$231.97	5.569%	$244.8884	$244.89	$244.90	$244.90
Purchase #3	$59.49	10.724%	$65.8697	$65.87	$65.85	$65.90
Purchase #4	$25.89	5.811%	$27.3945	$27.39	$27.40	$27.40
Purchase #5	$191.69	13.109%	$216.8186	$216.82	$216.80	$216.80
Purchase #6	$158.56	9.178%	$173.1126	$173.11	$173.10	$173.10
Purchase #7	$194.43	5.655%	$205.425	$205.43	$205.45	$205.40
7 purchase totals =	$919.76		$998.2963	$998.30	$998.30	$998.30