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	$188.61	6.351%	$200.5886	$200.59	$200.60	$200.60
Purchase #2	$51.99	6.850%	$55.5513	$55.55	$55.55	$55.60
Purchase #3	$118.81	8.133%	$128.4728	$128.47	$128.45	$128.50
Purchase #4	$152.92	3.852%	$158.8105	$158.81	$158.80	$158.80
Purchase #5	$78.63	6.713%	$83.9084	$83.91	$83.90	$83.90
Purchase #6	$239.73	4.290%	$250.0144	$250.01	$250.00	$250.00
Purchase #7	$36.73	4.784%	$38.4872	$38.49	$38.50	$38.50
7 purchase totals =	$867.42		$915.8332	$915.83	$915.80	$915.90