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	$40.54	9.631%	$44.4444	$44.44	$44.45	$44.40
Purchase #2	$179.70	7.262%	$192.7498	$192.75	$192.75	$192.70
Purchase #3	$206.98	9.422%	$226.4817	$226.48	$226.50	$226.50
Purchase #4	$61.69	9.262%	$67.4037	$67.40	$67.40	$67.40
Purchase #5	$35.67	8.141%	$38.5739	$38.57	$38.55	$38.60
Purchase #6	$141.31	6.482%	$150.4697	$150.47	$150.45	$150.50
Purchase #7	$131.94	9.383%	$144.3199	$144.32	$144.30	$144.30
7 purchase totals =	$797.83		$864.4431	$864.43	$864.40	$864.40