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	$38.48	10.415%	$42.4877	$42.49	$42.50	$42.50
Purchase #2	$235.65	4.487%	$246.2236	$246.22	$246.20	$246.20
Purchase #3	$226.25	6.730%	$241.4766	$241.48	$241.50	$241.50
Purchase #4	$132.85	4.304%	$138.5679	$138.57	$138.55	$138.60
Purchase #5	$247.49	3.290%	$255.6324	$255.63	$255.65	$255.60
Purchase #6	$37.74	9.240%	$41.2272	$41.23	$41.25	$41.20
Purchase #7	$101.96	3.469%	$105.497	$105.50	$105.50	$105.50
7 purchase totals =	$1,020.42		$1,071.1124	$1,071.12	$1,071.15	$1,071.10