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	$242.61	12.430%	$272.7664	$272.77	$272.75	$272.80
Purchase #2	$109.44	6.477%	$116.5284	$116.53	$116.55	$116.50
Purchase #3	$73.70	6.467%	$78.4662	$78.47	$78.45	$78.50
Purchase #4	$36.32	7.582%	$39.0738	$39.07	$39.05	$39.10
Purchase #5	$64.25	11.413%	$71.5829	$71.58	$71.60	$71.60
Purchase #6	$217.64	13.536%	$247.0998	$247.10	$247.10	$247.10
Purchase #7	$215.41	4.734%	$225.6075	$225.61	$225.60	$225.60
7 purchase totals =	$959.37		$1,051.1250	$1,051.13	$1,051.10	$1,051.20