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	$233.82	6.326%	$248.6115	$248.61	$248.60	$248.60
Purchase #2	$41.25	6.210%	$43.8116	$43.81	$43.80	$43.80
Purchase #3	$195.65	5.710%	$206.8216	$206.82	$206.80	$206.80
Purchase #4	$131.86	10.346%	$145.5022	$145.50	$145.50	$145.50
Purchase #5	$179.27	7.554%	$192.8121	$192.81	$192.80	$192.80
Purchase #6	$35.81	7.389%	$38.456	$38.46	$38.45	$38.50
Purchase #7	$180.93	5.259%	$190.4451	$190.45	$190.45	$190.40
7 purchase totals =	$998.59		$1,066.4601	$1,066.46	$1,066.40	$1,066.40