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	$65.50	4.554%	$68.4829	$68.48	$68.50	$68.50
Purchase #2	$62.84	7.189%	$67.3576	$67.36	$67.35	$67.40
Purchase #3	$37.89	7.264%	$40.6423	$40.64	$40.65	$40.60
Purchase #4	$86.26	7.462%	$92.6967	$92.70	$92.70	$92.70
Purchase #5	$135.32	4.870%	$141.9101	$141.91	$141.90	$141.90
Purchase #6	$107.49	7.532%	$115.5861	$115.59	$115.60	$115.60
Purchase #7	$126.89	10.248%	$139.8937	$139.89	$139.90	$139.90
7 purchase totals =	$622.19		$666.5694	$666.57	$666.60	$666.60