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	$139.43	9.446%	$152.6006	$152.60	$152.60	$152.60
Purchase #2	$113.79	13.179%	$128.7864	$128.79	$128.80	$128.80
Purchase #3	$39.98	7.665%	$43.0445	$43.04	$43.05	$43.00
Purchase #4	$169.34	8.790%	$184.225	$184.23	$184.25	$184.20
Purchase #5	$123.92	3.228%	$127.9201	$127.92	$127.90	$127.90
Purchase #6	$59.51	13.135%	$67.3266	$67.33	$67.35	$67.30
Purchase #7	$17.26	4.246%	$17.9929	$17.99	$18.00	$18.00
7 purchase totals =	$663.23		$721.8961	$721.90	$721.95	$721.80