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	$202.85	13.278%	$229.7844	$229.78	$229.80	$229.80
Purchase #2	$17.98	12.715%	$20.2662	$20.27	$20.25	$20.30
Purchase #3	$72.89	8.273%	$78.9202	$78.92	$78.90	$78.90
Purchase #4	$73.62	6.801%	$78.6269	$78.63	$78.65	$78.60
Purchase #5	$54.62	9.762%	$59.952	$59.95	$59.95	$60.00
Purchase #6	$184.34	6.806%	$196.8862	$196.89	$196.90	$196.90
Purchase #7	$12.54	10.329%	$13.8353	$13.84	$13.85	$13.80
7 purchase totals =	$618.84		$678.2712	$678.28	$678.30	$678.30