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	$45.51	12.147%	$51.0381	$51.04	$51.05	$51.00
Purchase #2	$42.52	8.842%	$46.2796	$46.28	$46.30	$46.30
Purchase #3	$130.33	7.863%	$140.5778	$140.58	$140.60	$140.60
Purchase #4	$93.39	3.369%	$96.5363	$96.54	$96.55	$96.50
Purchase #5	$108.55	13.522%	$123.2281	$123.23	$123.25	$123.20
Purchase #6	$88.80	13.695%	$100.9612	$100.96	$100.95	$101.00
Purchase #7	$82.84	10.416%	$91.4686	$91.47	$91.45	$91.50
7 purchase totals =	$591.94		$650.0897	$650.10	$650.15	$650.10