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	$91.59	9.697%	$100.4715	$100.47	$100.45	$100.50
Purchase #2	$103.25	5.310%	$108.7326	$108.73	$108.75	$108.70
Purchase #3	$220.86	11.764%	$246.842	$246.84	$246.85	$246.80
Purchase #4	$223.57	8.330%	$242.1934	$242.19	$242.20	$242.20
Purchase #5	$155.49	3.278%	$160.587	$160.59	$160.60	$160.60
Purchase #6	$162.30	6.547%	$172.9258	$172.93	$172.95	$172.90
Purchase #7	$62.90	12.611%	$70.8323	$70.83	$70.85	$70.80
7 purchase totals =	$1,019.96		$1,102.5846	$1,102.58	$1,102.65	$1,102.50