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	$178.38	12.154%	$200.0603	$200.06	$200.05	$200.10
Purchase #2	$101.43	6.641%	$108.166	$108.17	$108.15	$108.20
Purchase #3	$141.75	3.331%	$146.4717	$146.47	$146.45	$146.50
Purchase #4	$148.44	13.484%	$168.4556	$168.46	$168.45	$168.50
Purchase #5	$19.51	6.666%	$20.8105	$20.81	$20.80	$20.80
Purchase #6	$74.62	5.429%	$78.6711	$78.67	$78.65	$78.70
Purchase #7	$184.87	10.477%	$204.2388	$204.24	$204.25	$204.20
7 purchase totals =	$849.00		$926.8740	$926.88	$926.80	$927.00