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	$195.28	7.604%	$210.1291	$210.13	$210.15	$210.10
Purchase #2	$169.77	12.185%	$190.4565	$190.46	$190.45	$190.50
Purchase #3	$83.60	5.786%	$88.4371	$88.44	$88.45	$88.40
Purchase #4	$192.42	4.140%	$200.3862	$200.39	$200.40	$200.40
Purchase #5	$40.70	6.304%	$43.2657	$43.27	$43.25	$43.30
Purchase #6	$24.29	4.414%	$25.3622	$25.36	$25.35	$25.40
Purchase #7	$98.75	13.367%	$111.9499	$111.95	$111.95	$111.90
7 purchase totals =	$804.81		$869.9867	$870.00	$870.00	$870.00