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	$19.72	4.218%	$20.5518	$20.55	$20.55	$20.60
Purchase #2	$117.85	9.139%	$128.6203	$128.62	$128.60	$128.60
Purchase #3	$206.31	6.748%	$220.2318	$220.23	$220.25	$220.20
Purchase #4	$242.94	7.403%	$260.9248	$260.92	$260.90	$260.90
Purchase #5	$60.34	4.700%	$63.176	$63.18	$63.20	$63.20
Purchase #6	$19.67	4.762%	$20.6067	$20.61	$20.60	$20.60
Purchase #7	$172.92	13.688%	$196.5893	$196.59	$196.60	$196.60
7 purchase totals =	$839.75		$910.7007	$910.70	$910.70	$910.70