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	$40.30	4.664%	$42.1796	$42.18	$42.20	$42.20
Purchase #2	$144.71	6.304%	$153.8325	$153.83	$153.85	$153.80
Purchase #3	$187.36	11.808%	$209.4835	$209.48	$209.50	$209.50
Purchase #4	$230.58	12.867%	$260.2487	$260.25	$260.25	$260.20
Purchase #5	$160.86	10.162%	$177.2066	$177.21	$177.20	$177.20
Purchase #6	$172.27	10.589%	$190.5117	$190.51	$190.50	$190.50
Purchase #7	$62.51	7.377%	$67.1214	$67.12	$67.10	$67.10
7 purchase totals =	$998.59		$1,100.5840	$1,100.58	$1,100.60	$1,100.50