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	$218.30	5.588%	$230.4986	$230.50	$230.50	$230.50
Purchase #2	$39.45	6.145%	$41.8742	$41.87	$41.85	$41.90
Purchase #3	$145.68	9.152%	$159.0126	$159.01	$159.00	$159.00
Purchase #4	$80.31	11.684%	$89.6934	$89.69	$89.70	$89.70
Purchase #5	$177.87	5.670%	$187.9552	$187.96	$187.95	$188.00
Purchase #6	$61.70	5.366%	$65.0108	$65.01	$65.00	$65.00
Purchase #7	$140.51	3.118%	$144.8911	$144.89	$144.90	$144.90
7 purchase totals =	$863.82		$918.9359	$918.93	$918.90	$919.00