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	$248.94	9.870%	$273.5104	$273.51	$273.50	$273.50
Purchase #2	$172.88	10.122%	$190.3789	$190.38	$190.40	$190.40
Purchase #3	$39.71	13.422%	$45.0399	$45.04	$45.05	$45.00
Purchase #4	$196.45	13.378%	$222.7311	$222.73	$222.75	$222.70
Purchase #5	$227.57	11.773%	$254.3618	$254.36	$254.35	$254.40
Purchase #6	$108.37	13.782%	$123.3056	$123.31	$123.30	$123.30
Purchase #7	$174.64	12.835%	$197.055	$197.06	$197.05	$197.10
7 purchase totals =	$1,168.56		$1,306.3827	$1,306.39	$1,306.40	$1,306.40