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	$77.54	11.191%	$86.2175	$86.22	$86.20	$86.20
Purchase #2	$64.36	11.660%	$71.8644	$71.86	$71.85	$71.90
Purchase #3	$18.55	7.339%	$19.9114	$19.91	$19.90	$19.90
Purchase #4	$221.78	8.850%	$241.4075	$241.41	$241.40	$241.40
Purchase #5	$16.85	9.339%	$18.4236	$18.42	$18.40	$18.40
Purchase #6	$161.85	13.547%	$183.7758	$183.78	$183.80	$183.80
Purchase #7	$17.40	4.549%	$18.1915	$18.19	$18.20	$18.20
7 purchase totals =	$578.33		$639.7917	$639.79	$639.75	$639.80