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	$98.40	3.758%	$102.0979	$102.10	$102.10	$102.10
Purchase #2	$55.61	6.675%	$59.322	$59.32	$59.30	$59.30
Purchase #3	$45.74	12.791%	$51.5906	$51.59	$51.60	$51.60
Purchase #4	$112.27	5.673%	$118.6391	$118.64	$118.65	$118.60
Purchase #5	$132.25	8.356%	$143.3008	$143.30	$143.30	$143.30
Purchase #6	$241.58	4.189%	$251.6998	$251.70	$251.70	$251.70
Purchase #7	$117.80	7.819%	$127.0108	$127.01	$127.00	$127.00
7 purchase totals =	$803.65		$853.6610	$853.66	$853.65	$853.60