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	$94.59	5.382%	$99.6808	$99.68	$99.70	$99.70
Purchase #2	$81.58	11.337%	$90.8287	$90.83	$90.85	$90.80
Purchase #3	$113.64	12.283%	$127.5984	$127.60	$127.60	$127.60
Purchase #4	$167.29	5.600%	$176.6582	$176.66	$176.65	$176.70
Purchase #5	$114.90	7.557%	$123.583	$123.58	$123.60	$123.60
Purchase #6	$105.46	3.539%	$109.1922	$109.19	$109.20	$109.20
Purchase #7	$110.37	11.171%	$122.6994	$122.70	$122.70	$122.70
7 purchase totals =	$787.83		$850.2407	$850.24	$850.30	$850.30