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	$131.54	4.617%	$137.6132	$137.61	$137.60	$137.60
Purchase #2	$92.58	5.166%	$97.3627	$97.36	$97.35	$97.40
Purchase #3	$55.33	11.777%	$61.8462	$61.85	$61.85	$61.80
Purchase #4	$106.58	4.161%	$111.0148	$111.01	$111.00	$111.00
Purchase #5	$147.65	3.664%	$153.0599	$153.06	$153.05	$153.10
Purchase #6	$62.60	4.830%	$65.6236	$65.62	$65.60	$65.60
Purchase #7	$13.30	7.244%	$14.2635	$14.26	$14.25	$14.30
7 purchase totals =	$609.58		$640.7839	$640.77	$640.70	$640.80