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	$231.45	8.202%	$250.4335	$250.43	$250.45	$250.40
Purchase #2	$142.34	8.390%	$154.2823	$154.28	$154.30	$154.30
Purchase #3	$71.90	11.848%	$80.4187	$80.42	$80.40	$80.40
Purchase #4	$206.81	8.555%	$224.5026	$224.50	$224.50	$224.50
Purchase #5	$144.83	6.202%	$153.8124	$153.81	$153.80	$153.80
Purchase #6	$133.92	7.710%	$144.2452	$144.25	$144.25	$144.20
Purchase #7	$177.91	10.656%	$196.8681	$196.87	$196.85	$196.90
7 purchase totals =	$1,109.16		$1,204.5628	$1,204.56	$1,204.55	$1,204.50