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	$245.39	11.308%	$273.1387	$273.14	$273.15	$273.10
Purchase #2	$190.59	9.227%	$208.1757	$208.18	$208.20	$208.20
Purchase #3	$17.38	5.171%	$18.2787	$18.28	$18.30	$18.30
Purchase #4	$143.52	5.199%	$150.9816	$150.98	$151.00	$151.00
Purchase #5	$192.92	10.844%	$213.8402	$213.84	$213.85	$213.80
Purchase #6	$15.43	11.661%	$17.2293	$17.23	$17.25	$17.20
Purchase #7	$77.92	10.188%	$85.8585	$85.86	$85.85	$85.90
7 purchase totals =	$883.15		$967.5027	$967.51	$967.60	$967.50