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	$43.85	9.199%	$47.8838	$47.88	$47.90	$47.90
Purchase #2	$242.63	11.462%	$270.4403	$270.44	$270.45	$270.40
Purchase #3	$122.57	12.606%	$138.0212	$138.02	$138.00	$138.00
Purchase #4	$129.28	10.868%	$143.3302	$143.33	$143.35	$143.30
Purchase #5	$94.87	13.299%	$107.4868	$107.49	$107.50	$107.50
Purchase #6	$200.85	5.765%	$212.429	$212.43	$212.45	$212.40
Purchase #7	$57.45	3.376%	$59.3895	$59.39	$59.40	$59.40
7 purchase totals =	$891.50		$978.9808	$978.98	$979.05	$978.90