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	$6.70	6.552%	$7.139	$7.14	$7.15	$7.10
Purchase #2	$146.76	9.589%	$160.8328	$160.83	$160.85	$160.80
Purchase #3	$157.78	6.801%	$168.5106	$168.51	$168.50	$168.50
Purchase #4	$161.75	3.486%	$167.3886	$167.39	$167.40	$167.40
Purchase #5	$64.79	13.766%	$73.709	$73.71	$73.70	$73.70
Purchase #6	$212.59	13.685%	$241.6829	$241.68	$241.70	$241.70
Purchase #7	$137.48	5.385%	$144.8833	$144.88	$144.90	$144.90
7 purchase totals =	$887.85		$964.1462	$964.14	$964.20	$964.10