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	$39.41	7.105%	$42.2101	$42.21	$42.20	$42.20
Purchase #2	$42.69	6.668%	$45.5366	$45.54	$45.55	$45.50
Purchase #3	$33.53	11.140%	$37.2652	$37.27	$37.25	$37.30
Purchase #4	$242.90	3.816%	$252.1691	$252.17	$252.15	$252.20
Purchase #5	$189.92	13.724%	$215.9846	$215.98	$216.00	$216.00
Purchase #6	$127.38	5.823%	$134.7973	$134.80	$134.80	$134.80
Purchase #7	$179.76	13.195%	$203.4793	$203.48	$203.50	$203.50
7 purchase totals =	$855.59		$931.4422	$931.45	$931.45	$931.50