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	$150.39	3.649%	$155.8777	$155.88	$155.90	$155.90
Purchase #2	$104.44	13.562%	$118.6042	$118.60	$118.60	$118.60
Purchase #3	$249.41	12.691%	$281.0626	$281.06	$281.05	$281.10
Purchase #4	$222.25	5.493%	$234.4582	$234.46	$234.45	$234.50
Purchase #5	$39.48	4.530%	$41.2684	$41.27	$41.25	$41.30
Purchase #6	$89.36	12.175%	$100.2396	$100.24	$100.25	$100.20
Purchase #7	$54.77	8.615%	$59.4884	$59.49	$59.50	$59.50
7 purchase totals =	$910.10		$990.9991	$991.00	$991.00	$991.10