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	$116.26	3.562%	$120.4012	$120.40	$120.40	$120.40
Purchase #2	$56.50	10.495%	$62.4297	$62.43	$62.45	$62.40
Purchase #3	$32.65	9.123%	$35.6287	$35.63	$35.65	$35.60
Purchase #4	$172.96	3.849%	$179.6172	$179.62	$179.60	$179.60
Purchase #5	$140.59	13.692%	$159.8396	$159.84	$159.85	$159.80
Purchase #6	$22.88	8.756%	$24.8834	$24.88	$24.90	$24.90
Purchase #7	$172.53	13.608%	$196.0079	$196.01	$196.00	$196.00
7 purchase totals =	$714.37		$778.8077	$778.81	$778.85	$778.70