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	$123.56	8.276%	$133.7858	$133.79	$133.80	$133.80
Purchase #2	$12.28	13.325%	$13.9163	$13.92	$13.90	$13.90
Purchase #3	$79.83	13.306%	$90.4522	$90.45	$90.45	$90.50
Purchase #4	$245.86	7.583%	$264.5036	$264.50	$264.50	$264.50
Purchase #5	$65.47	12.393%	$73.5837	$73.58	$73.60	$73.60
Purchase #6	$34.54	6.497%	$36.7841	$36.78	$36.80	$36.80
Purchase #7	$90.82	4.772%	$95.1539	$95.15	$95.15	$95.20
7 purchase totals =	$652.36		$708.1796	$708.17	$708.20	$708.30