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	$15.87	12.265%	$17.8165	$17.82	$17.80	$17.80
Purchase #2	$51.94	6.561%	$55.3478	$55.35	$55.35	$55.30
Purchase #3	$21.32	7.335%	$22.8838	$22.88	$22.90	$22.90
Purchase #4	$39.72	10.520%	$43.8985	$43.90	$43.90	$43.90
Purchase #5	$96.31	4.707%	$100.8433	$100.84	$100.85	$100.80
Purchase #6	$205.90	4.220%	$214.589	$214.59	$214.60	$214.60
Purchase #7	$38.84	9.190%	$42.4094	$42.41	$42.40	$42.40
7 purchase totals =	$469.90		$497.7883	$497.79	$497.80	$497.70