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	$160.29	3.741%	$166.2864	$166.29	$166.30	$166.30
Purchase #2	$78.89	8.820%	$85.8481	$85.85	$85.85	$85.80
Purchase #3	$23.26	4.418%	$24.2876	$24.29	$24.30	$24.30
Purchase #4	$189.28	5.313%	$199.3364	$199.34	$199.35	$199.30
Purchase #5	$88.94	8.585%	$96.5755	$96.58	$96.60	$96.60
Purchase #6	$242.77	5.375%	$255.8189	$255.82	$255.80	$255.80
Purchase #7	$36.31	11.337%	$40.4265	$40.43	$40.45	$40.40
7 purchase totals =	$819.74		$868.5794	$868.60	$868.65	$868.50