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	$123.29	9.415%	$134.8978	$134.90	$134.90	$134.90
Purchase #2	$160.51	7.301%	$172.2288	$172.23	$172.25	$172.20
Purchase #3	$142.92	13.380%	$162.0427	$162.04	$162.05	$162.00
Purchase #4	$111.44	4.627%	$116.5963	$116.60	$116.60	$116.60
Purchase #5	$68.32	12.368%	$76.7698	$76.77	$76.75	$76.80
Purchase #6	$189.57	8.410%	$205.5128	$205.51	$205.50	$205.50
Purchase #7	$49.34	11.195%	$54.8636	$54.86	$54.85	$54.90
7 purchase totals =	$845.39		$922.9118	$922.91	$922.90	$922.90