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	$16.96	11.325%	$18.8807	$18.88	$18.90	$18.90
Purchase #2	$84.79	9.118%	$92.5212	$92.52	$92.50	$92.50
Purchase #3	$145.89	8.249%	$157.9245	$157.92	$157.90	$157.90
Purchase #4	$229.39	9.197%	$250.487	$250.49	$250.50	$250.50
Purchase #5	$192.95	13.424%	$218.8516	$218.85	$218.85	$218.90
Purchase #6	$224.69	10.658%	$248.6375	$248.64	$248.65	$248.60
Purchase #7	$51.81	4.123%	$53.9461	$53.95	$53.95	$53.90
7 purchase totals =	$946.48		$1,041.2486	$1,041.25	$1,041.25	$1,041.20