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	$27.60	3.700%	$28.6212	$28.62	$28.60	$28.60
Purchase #2	$25.65	13.224%	$29.042	$29.04	$29.05	$29.00
Purchase #3	$23.28	11.280%	$25.906	$25.91	$25.90	$25.90
Purchase #4	$195.86	11.576%	$218.5328	$218.53	$218.55	$218.50
Purchase #5	$101.84	9.518%	$111.5331	$111.53	$111.55	$111.50
Purchase #6	$90.34	13.116%	$102.189	$102.19	$102.20	$102.20
Purchase #7	$189.70	11.693%	$211.8816	$211.88	$211.90	$211.90
7 purchase totals =	$654.27		$727.7057	$727.70	$727.75	$727.60