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	$61.63	5.729%	$65.1608	$65.16	$65.15	$65.20
Purchase #2	$193.76	8.129%	$209.5108	$209.51	$209.50	$209.50
Purchase #3	$186.93	7.471%	$200.8955	$200.90	$200.90	$200.90
Purchase #4	$23.66	4.285%	$24.6738	$24.67	$24.65	$24.70
Purchase #5	$12.38	11.757%	$13.8355	$13.84	$13.85	$13.80
Purchase #6	$87.81	13.417%	$99.5915	$99.59	$99.60	$99.60
Purchase #7	$170.65	5.384%	$179.8378	$179.84	$179.85	$179.80
7 purchase totals =	$736.82		$793.5057	$793.51	$793.50	$793.50