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	$45.41	11.258%	$50.5223	$50.52	$50.50	$50.50
Purchase #2	$96.31	11.754%	$107.6303	$107.63	$107.65	$107.60
Purchase #3	$192.70	4.649%	$201.6586	$201.66	$201.65	$201.70
Purchase #4	$147.50	11.742%	$164.8195	$164.82	$164.80	$164.80
Purchase #5	$50.44	13.147%	$57.0713	$57.07	$57.05	$57.10
Purchase #6	$94.69	6.268%	$100.6252	$100.63	$100.65	$100.60
Purchase #7	$112.45	13.540%	$127.6757	$127.68	$127.70	$127.70
7 purchase totals =	$739.50		$810.0029	$810.01	$810.00	$810.00