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	$51.94	6.394%	$55.261	$55.26	$55.25	$55.30
Purchase #2	$61.86	7.176%	$66.2991	$66.30	$66.30	$66.30
Purchase #3	$92.98	3.683%	$96.4045	$96.40	$96.40	$96.40
Purchase #4	$95.54	6.583%	$101.8294	$101.83	$101.85	$101.80
Purchase #5	$126.74	3.818%	$131.5789	$131.58	$131.60	$131.60
Purchase #6	$27.66	4.437%	$28.8873	$28.89	$28.90	$28.90
Purchase #7	$173.82	8.675%	$188.8989	$188.90	$188.90	$188.90
7 purchase totals =	$630.54		$669.1591	$669.16	$669.20	$669.20