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	$130.74	5.177%	$137.5084	$137.51	$137.50	$137.50
Purchase #2	$177.90	11.627%	$198.5844	$198.58	$198.60	$198.60
Purchase #3	$53.93	9.690%	$59.1558	$59.16	$59.15	$59.20
Purchase #4	$172.96	3.367%	$178.7836	$178.78	$178.80	$178.80
Purchase #5	$96.91	3.381%	$100.1865	$100.19	$100.20	$100.20
Purchase #6	$173.91	5.109%	$182.7951	$182.80	$182.80	$182.80
Purchase #7	$44.60	7.190%	$47.8067	$47.81	$47.80	$47.80
7 purchase totals =	$850.95		$904.8205	$904.83	$904.85	$904.90