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	$151.60	5.167%	$159.4332	$159.43	$159.45	$159.40
Purchase #2	$49.80	13.385%	$56.4657	$56.47	$56.45	$56.50
Purchase #3	$84.72	12.767%	$95.5362	$95.54	$95.55	$95.50
Purchase #4	$19.54	3.345%	$20.1936	$20.19	$20.20	$20.20
Purchase #5	$208.91	6.355%	$222.1862	$222.19	$222.20	$222.20
Purchase #6	$117.74	4.712%	$123.2879	$123.29	$123.30	$123.30
Purchase #7	$78.37	9.423%	$85.7548	$85.75	$85.75	$85.80
7 purchase totals =	$710.68		$762.8576	$762.86	$762.90	$762.90