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	$108.93	10.329%	$120.1814	$120.18	$120.20	$120.20
Purchase #2	$29.49	9.859%	$32.3974	$32.40	$32.40	$32.40
Purchase #3	$237.30	8.303%	$257.003	$257.00	$257.00	$257.00
Purchase #4	$35.76	5.312%	$37.6596	$37.66	$37.65	$37.70
Purchase #5	$170.97	12.658%	$192.6114	$192.61	$192.60	$192.60
Purchase #6	$69.59	12.564%	$78.3333	$78.33	$78.35	$78.30
Purchase #7	$115.85	13.231%	$131.1781	$131.18	$131.20	$131.20
7 purchase totals =	$767.89		$849.3642	$849.36	$849.40	$849.40