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	$246.86	3.125%	$254.5744	$254.57	$254.55	$254.60
Purchase #2	$92.65	13.320%	$104.991	$104.99	$105.00	$105.00
Purchase #3	$90.92	10.651%	$100.6039	$100.60	$100.60	$100.60
Purchase #4	$59.67	7.625%	$64.2198	$64.22	$64.20	$64.20
Purchase #5	$78.71	12.569%	$88.6031	$88.60	$88.60	$88.60
Purchase #6	$102.59	9.422%	$112.256	$112.26	$112.25	$112.30
Purchase #7	$67.64	3.728%	$70.1616	$70.16	$70.15	$70.20
7 purchase totals =	$739.04		$795.4098	$795.40	$795.35	$795.50