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	$38.92	11.803%	$43.5137	$43.51	$43.50	$43.50
Purchase #2	$141.34	3.263%	$145.9519	$145.95	$145.95	$146.00
Purchase #3	$164.40	5.177%	$172.911	$172.91	$172.90	$172.90
Purchase #4	$198.58	13.537%	$225.4618	$225.46	$225.45	$225.50
Purchase #5	$113.86	9.344%	$124.4991	$124.50	$124.50	$124.50
Purchase #6	$28.77	13.254%	$32.5832	$32.58	$32.60	$32.60
Purchase #7	$53.43	10.799%	$59.1999	$59.20	$59.20	$59.20
7 purchase totals =	$739.30		$804.1206	$804.11	$804.10	$804.20