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	$199.98	10.367%	$220.7119	$220.71	$220.70	$220.70
Purchase #2	$177.46	12.296%	$199.2805	$199.28	$199.30	$199.30
Purchase #3	$126.96	3.859%	$131.8594	$131.86	$131.85	$131.90
Purchase #4	$167.26	8.522%	$181.5139	$181.51	$181.50	$181.50
Purchase #5	$60.25	12.433%	$67.7409	$67.74	$67.75	$67.70
Purchase #6	$208.36	6.206%	$221.2908	$221.29	$221.30	$221.30
Purchase #7	$79.31	13.495%	$90.0129	$90.01	$90.00	$90.00
7 purchase totals =	$1,019.58		$1,112.4103	$1,112.40	$1,112.40	$1,112.40