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	$17.39	5.314%	$18.3141	$18.31	$18.30	$18.30
Purchase #2	$26.25	8.248%	$28.4151	$28.42	$28.40	$28.40
Purchase #3	$96.27	8.517%	$104.4693	$104.47	$104.45	$104.50
Purchase #4	$69.35	13.138%	$78.4612	$78.46	$78.45	$78.50
Purchase #5	$218.67	4.547%	$228.6129	$228.61	$228.60	$228.60
Purchase #6	$214.27	3.603%	$221.9901	$221.99	$222.00	$222.00
Purchase #7	$56.65	5.238%	$59.6173	$59.62	$59.60	$59.60
7 purchase totals =	$698.85		$739.8800	$739.88	$739.80	$739.90