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	$5.28	13.597%	$5.9979	$6.00	$6.00	$6.00
Purchase #2	$70.61	11.725%	$78.889	$78.89	$78.90	$78.90
Purchase #3	$112.79	7.125%	$120.8263	$120.83	$120.85	$120.80
Purchase #4	$172.82	8.734%	$187.9141	$187.91	$187.90	$187.90
Purchase #5	$133.54	5.496%	$140.8794	$140.88	$140.90	$140.90
Purchase #6	$131.30	8.189%	$142.0522	$142.05	$142.05	$142.10
Purchase #7	$82.88	10.598%	$91.6636	$91.66	$91.65	$91.70
7 purchase totals =	$709.22		$768.2225	$768.22	$768.25	$768.30