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	$117.49	8.509%	$127.4872	$127.49	$127.50	$127.50
Purchase #2	$58.54	11.123%	$65.0514	$65.05	$65.05	$65.10
Purchase #3	$143.45	11.812%	$160.3943	$160.39	$160.40	$160.40
Purchase #4	$196.92	7.639%	$211.9627	$211.96	$211.95	$212.00
Purchase #5	$179.92	5.842%	$190.4309	$190.43	$190.45	$190.40
Purchase #6	$36.44	5.644%	$38.4967	$38.50	$38.50	$38.50
Purchase #7	$98.83	11.134%	$109.8337	$109.83	$109.85	$109.80
7 purchase totals =	$831.59		$903.6569	$903.65	$903.70	$903.70