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	$19.33	7.706%	$20.8196	$20.82	$20.80	$20.80
Purchase #2	$139.99	8.638%	$152.0823	$152.08	$152.10	$152.10
Purchase #3	$215.33	10.140%	$237.1645	$237.16	$237.15	$237.20
Purchase #4	$44.52	12.534%	$50.1001	$50.10	$50.10	$50.10
Purchase #5	$126.50	4.197%	$131.8092	$131.81	$131.80	$131.80
Purchase #6	$148.76	13.707%	$169.1505	$169.15	$169.15	$169.20
Purchase #7	$196.27	12.786%	$221.3651	$221.37	$221.35	$221.40
7 purchase totals =	$890.70		$982.4913	$982.49	$982.45	$982.60