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	$40.89	3.686%	$42.3972	$42.40	$42.40	$42.40
Purchase #2	$165.73	3.622%	$171.7327	$171.73	$171.75	$171.70
Purchase #3	$78.68	5.632%	$83.1113	$83.11	$83.10	$83.10
Purchase #4	$62.58	4.132%	$65.1658	$65.17	$65.15	$65.20
Purchase #5	$41.28	4.321%	$43.0637	$43.06	$43.05	$43.10
Purchase #6	$158.55	8.761%	$172.4406	$172.44	$172.45	$172.40
Purchase #7	$139.39	4.580%	$145.7741	$145.77	$145.75	$145.80
7 purchase totals =	$687.10		$723.6854	$723.68	$723.65	$723.70