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	$45.80	13.282%	$51.8832	$51.88	$51.90	$51.90
Purchase #2	$111.61	13.651%	$126.8459	$126.85	$126.85	$126.80
Purchase #3	$184.35	12.816%	$207.9763	$207.98	$208.00	$208.00
Purchase #4	$199.51	11.435%	$222.324	$222.32	$222.30	$222.30
Purchase #5	$193.65	13.688%	$220.1568	$220.16	$220.15	$220.20
Purchase #6	$95.41	5.280%	$100.4476	$100.45	$100.45	$100.40
Purchase #7	$35.39	13.454%	$40.1514	$40.15	$40.15	$40.20
7 purchase totals =	$865.72		$969.7852	$969.79	$969.80	$969.80