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	$63.43	12.757%	$71.5218	$71.52	$71.50	$71.50
Purchase #2	$150.46	12.197%	$168.8116	$168.81	$168.80	$168.80
Purchase #3	$87.77	11.449%	$97.8188	$97.82	$97.80	$97.80
Purchase #4	$203.41	3.151%	$209.8194	$209.82	$209.80	$209.80
Purchase #5	$139.86	9.533%	$153.1929	$153.19	$153.20	$153.20
Purchase #6	$117.49	8.235%	$127.1653	$127.17	$127.15	$127.20
Purchase #7	$151.99	13.119%	$171.9296	$171.93	$171.95	$171.90
7 purchase totals =	$914.41		$1,000.2594	$1,000.26	$1,000.20	$1,000.20