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	$240.37	11.285%	$267.4958	$267.50	$267.50	$267.50
Purchase #2	$43.89	5.755%	$46.4159	$46.42	$46.40	$46.40
Purchase #3	$117.82	5.550%	$124.359	$124.36	$124.35	$124.40
Purchase #4	$172.55	7.640%	$185.7328	$185.73	$185.75	$185.70
Purchase #5	$128.50	9.756%	$141.0365	$141.04	$141.05	$141.00
Purchase #6	$40.64	7.766%	$43.7961	$43.80	$43.80	$43.80
Purchase #7	$170.29	7.131%	$182.4334	$182.43	$182.45	$182.40
7 purchase totals =	$914.06		$991.2695	$991.28	$991.30	$991.20