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	$108.67	9.664%	$119.1719	$119.17	$119.15	$119.20
Purchase #2	$85.47	5.587%	$90.2452	$90.25	$90.25	$90.20
Purchase #3	$42.27	4.762%	$44.2829	$44.28	$44.30	$44.30
Purchase #4	$32.92	5.648%	$34.7793	$34.78	$34.80	$34.80
Purchase #5	$95.71	3.757%	$99.3058	$99.31	$99.30	$99.30
Purchase #6	$147.49	4.718%	$154.4486	$154.45	$154.45	$154.40
Purchase #7	$14.81	7.608%	$15.9367	$15.94	$15.95	$15.90
7 purchase totals =	$527.34		$558.1704	$558.18	$558.20	$558.10