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	$240.83	6.492%	$256.4647	$256.46	$256.45	$256.50
Purchase #2	$101.77	3.856%	$105.6943	$105.69	$105.70	$105.70
Purchase #3	$114.50	10.789%	$126.8534	$126.85	$126.85	$126.90
Purchase #4	$64.35	9.778%	$70.6421	$70.64	$70.65	$70.60
Purchase #5	$159.85	4.744%	$167.4333	$167.43	$167.45	$167.40
Purchase #6	$152.76	11.634%	$170.5321	$170.53	$170.55	$170.50
Purchase #7	$244.96	11.633%	$273.4562	$273.46	$273.45	$273.50
7 purchase totals =	$1,079.02		$1,171.0761	$1,171.06	$1,171.10	$1,171.10