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	$206.40	9.233%	$225.4569	$225.46	$225.45	$225.50
Purchase #2	$37.84	12.120%	$42.4262	$42.43	$42.45	$42.40
Purchase #3	$157.52	10.563%	$174.1588	$174.16	$174.15	$174.20
Purchase #4	$28.89	13.837%	$32.8875	$32.89	$32.90	$32.90
Purchase #5	$49.43	3.558%	$51.1887	$51.19	$51.20	$51.20
Purchase #6	$42.72	4.868%	$44.7996	$44.80	$44.80	$44.80
Purchase #7	$144.27	4.369%	$150.5732	$150.57	$150.55	$150.60
7 purchase totals =	$667.07		$721.4909	$721.50	$721.50	$721.60