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	$65.89	3.429%	$68.1494	$68.15	$68.15	$68.10
Purchase #2	$86.35	13.504%	$98.0107	$98.01	$98.00	$98.00
Purchase #3	$153.43	5.642%	$162.0865	$162.09	$162.10	$162.10
Purchase #4	$71.38	4.508%	$74.5978	$74.60	$74.60	$74.60
Purchase #5	$61.55	8.600%	$66.8433	$66.84	$66.85	$66.80
Purchase #6	$75.58	12.535%	$85.054	$85.05	$85.05	$85.10
Purchase #7	$91.61	8.624%	$99.5104	$99.51	$99.50	$99.50
7 purchase totals =	$605.79		$654.2521	$654.25	$654.25	$654.20