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	$217.77	11.353%	$242.4934	$242.49	$242.50	$242.50
Purchase #2	$132.27	3.801%	$137.2976	$137.30	$137.30	$137.30
Purchase #3	$157.69	13.163%	$178.4467	$178.45	$178.45	$178.40
Purchase #4	$238.79	7.840%	$257.5111	$257.51	$257.50	$257.50
Purchase #5	$194.76	9.617%	$213.4901	$213.49	$213.50	$213.50
Purchase #6	$70.31	3.665%	$72.8869	$72.89	$72.90	$72.90
Purchase #7	$177.44	4.706%	$185.7903	$185.79	$185.80	$185.80
7 purchase totals =	$1,189.03		$1,287.9161	$1,287.92	$1,287.95	$1,287.90