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	$131.27	4.315%	$136.9343	$136.93	$136.95	$136.90
Purchase #2	$132.81	6.793%	$141.8318	$141.83	$141.85	$141.80
Purchase #3	$225.28	11.521%	$251.2345	$251.23	$251.25	$251.20
Purchase #4	$124.64	3.208%	$128.6385	$128.64	$128.65	$128.60
Purchase #5	$76.49	6.407%	$81.3907	$81.39	$81.40	$81.40
Purchase #6	$66.71	7.277%	$71.5645	$71.56	$71.55	$71.60
Purchase #7	$145.73	12.545%	$164.0118	$164.01	$164.00	$164.00
7 purchase totals =	$902.93		$975.6061	$975.59	$975.65	$975.50