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	$144.84	13.362%	$164.1935	$164.19	$164.20	$164.20
Purchase #2	$185.76	11.178%	$206.5243	$206.52	$206.50	$206.50
Purchase #3	$177.26	11.621%	$197.8594	$197.86	$197.85	$197.90
Purchase #4	$231.69	10.280%	$255.5077	$255.51	$255.50	$255.50
Purchase #5	$80.67	3.839%	$83.7669	$83.77	$83.75	$83.80
Purchase #6	$46.89	13.866%	$53.3918	$53.39	$53.40	$53.40
Purchase #7	$149.35	12.376%	$167.8336	$167.83	$167.85	$167.80
7 purchase totals =	$1,016.46		$1,129.0772	$1,129.07	$1,129.05	$1,129.10