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	$48.35	6.773%	$51.6247	$51.62	$51.60	$51.60
Purchase #2	$153.80	8.786%	$167.3129	$167.31	$167.30	$167.30
Purchase #3	$43.31	4.282%	$45.1645	$45.16	$45.15	$45.20
Purchase #4	$73.39	13.116%	$83.0158	$83.02	$83.00	$83.00
Purchase #5	$51.56	9.189%	$56.2978	$56.30	$56.30	$56.30
Purchase #6	$149.78	10.320%	$165.2373	$165.24	$165.25	$165.20
Purchase #7	$234.32	6.719%	$250.064	$250.06	$250.05	$250.10
7 purchase totals =	$754.51		$818.7170	$818.71	$818.65	$818.70