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	$137.41	4.292%	$143.3076	$143.31	$143.30	$143.30
Purchase #2	$131.87	9.516%	$144.4187	$144.42	$144.40	$144.40
Purchase #3	$144.61	9.552%	$158.4231	$158.42	$158.40	$158.40
Purchase #4	$142.25	11.446%	$158.5319	$158.53	$158.55	$158.50
Purchase #5	$18.43	5.301%	$19.407	$19.41	$19.40	$19.40
Purchase #6	$141.32	6.371%	$150.3235	$150.32	$150.30	$150.30
Purchase #7	$166.97	11.102%	$185.507	$185.51	$185.50	$185.50
7 purchase totals =	$882.86		$959.9188	$959.92	$959.85	$959.80