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	$66.72	11.382%	$74.3141	$74.31	$74.30	$74.30
Purchase #2	$73.49	6.734%	$78.4388	$78.44	$78.45	$78.40
Purchase #3	$73.76	10.611%	$81.5867	$81.59	$81.60	$81.60
Purchase #4	$191.39	5.396%	$201.7174	$201.72	$201.70	$201.70
Purchase #5	$86.81	13.520%	$98.5467	$98.55	$98.55	$98.50
Purchase #6	$67.34	6.187%	$71.5063	$71.51	$71.50	$71.50
Purchase #7	$41.89	10.844%	$46.4326	$46.43	$46.45	$46.40
7 purchase totals =	$601.40		$652.5426	$652.55	$652.55	$652.40