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	$45.63	5.869%	$48.308	$48.31	$48.30	$48.30
Purchase #2	$175.53	6.465%	$186.878	$186.88	$186.90	$186.90
Purchase #3	$132.66	5.390%	$139.8104	$139.81	$139.80	$139.80
Purchase #4	$38.62	9.191%	$42.1696	$42.17	$42.15	$42.20
Purchase #5	$102.83	8.724%	$111.8009	$111.80	$111.80	$111.80
Purchase #6	$18.50	8.751%	$20.1189	$20.12	$20.10	$20.10
Purchase #7	$79.86	4.514%	$83.4649	$83.46	$83.45	$83.50
7 purchase totals =	$593.63		$632.5507	$632.55	$632.50	$632.60