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	$84.86	5.226%	$89.2948	$89.29	$89.30	$89.30
Purchase #2	$214.37	13.341%	$242.9691	$242.97	$242.95	$243.00
Purchase #3	$150.90	11.752%	$168.6338	$168.63	$168.65	$168.60
Purchase #4	$238.81	4.243%	$248.9427	$248.94	$248.95	$248.90
Purchase #5	$131.59	3.717%	$136.4812	$136.48	$136.50	$136.50
Purchase #6	$49.72	5.825%	$52.6162	$52.62	$52.60	$52.60
Purchase #7	$121.92	10.668%	$134.9264	$134.93	$134.95	$134.90
7 purchase totals =	$992.17		$1,073.8642	$1,073.86	$1,073.90	$1,073.80