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	$225.46	9.588%	$247.0771	$247.08	$247.10	$247.10
Purchase #2	$115.38	11.124%	$128.2149	$128.21	$128.20	$128.20
Purchase #3	$248.28	13.493%	$281.7804	$281.78	$281.80	$281.80
Purchase #4	$61.34	10.640%	$67.8666	$67.87	$67.85	$67.90
Purchase #5	$11.89	12.227%	$13.3438	$13.34	$13.35	$13.30
Purchase #6	$191.99	11.706%	$214.4643	$214.46	$214.45	$214.50
Purchase #7	$48.71	4.434%	$50.8698	$50.87	$50.85	$50.90
7 purchase totals =	$903.05		$1,003.6169	$1,003.61	$1,003.60	$1,003.70