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	$61.86	9.706%	$67.8641	$67.86	$67.85	$67.90
Purchase #2	$216.57	11.176%	$240.7739	$240.77	$240.75	$240.80
Purchase #3	$51.76	10.610%	$57.2517	$57.25	$57.25	$57.30
Purchase #4	$93.53	7.448%	$100.4961	$100.50	$100.50	$100.50
Purchase #5	$192.34	6.353%	$204.5594	$204.56	$204.55	$204.60
Purchase #6	$167.92	13.513%	$190.611	$190.61	$190.60	$190.60
Purchase #7	$64.76	6.437%	$68.9286	$68.93	$68.95	$68.90
7 purchase totals =	$848.74		$930.4848	$930.48	$930.45	$930.60