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	$168.81	6.386%	$179.5902	$179.59	$179.60	$179.60
Purchase #2	$233.68	12.342%	$262.5208	$262.52	$262.50	$262.50
Purchase #3	$26.76	7.393%	$28.7384	$28.74	$28.75	$28.70
Purchase #4	$104.80	13.337%	$118.7772	$118.78	$118.80	$118.80
Purchase #5	$37.31	12.396%	$41.9349	$41.93	$41.95	$41.90
Purchase #6	$59.89	10.215%	$66.0078	$66.01	$66.00	$66.00
Purchase #7	$236.62	11.370%	$263.5237	$263.52	$263.50	$263.50
7 purchase totals =	$867.87		$961.0930	$961.09	$961.10	$961.00