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	$223.69	8.392%	$242.4621	$242.46	$242.45	$242.50
Purchase #2	$126.52	6.274%	$134.4579	$134.46	$134.45	$134.50
Purchase #3	$165.77	4.332%	$172.9512	$172.95	$172.95	$173.00
Purchase #4	$86.86	10.472%	$95.956	$95.96	$95.95	$96.00
Purchase #5	$50.56	3.760%	$52.4611	$52.46	$52.45	$52.50
Purchase #6	$104.66	10.860%	$116.0261	$116.03	$116.05	$116.00
Purchase #7	$80.82	9.641%	$88.6119	$88.61	$88.60	$88.60
7 purchase totals =	$838.88		$902.9263	$902.93	$902.90	$903.10