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	$36.72	4.531%	$38.3838	$38.38	$38.40	$38.40
Purchase #2	$132.61	6.395%	$141.0904	$141.09	$141.10	$141.10
Purchase #3	$41.67	6.324%	$44.3052	$44.31	$44.30	$44.30
Purchase #4	$83.98	6.282%	$89.2556	$89.26	$89.25	$89.30
Purchase #5	$147.49	8.805%	$160.4765	$160.48	$160.50	$160.50
Purchase #6	$128.55	8.491%	$139.4652	$139.47	$139.45	$139.50
Purchase #7	$178.27	3.572%	$184.6378	$184.64	$184.65	$184.60
7 purchase totals =	$749.29		$797.6145	$797.63	$797.65	$797.70