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	$150.34	11.353%	$167.4081	$167.41	$167.40	$167.40
Purchase #2	$116.76	13.577%	$132.6125	$132.61	$132.60	$132.60
Purchase #3	$72.48	7.867%	$78.182	$78.18	$78.20	$78.20
Purchase #4	$46.75	7.541%	$50.2754	$50.28	$50.30	$50.30
Purchase #5	$107.53	10.632%	$118.9626	$118.96	$118.95	$119.00
Purchase #6	$179.37	6.202%	$190.4945	$190.49	$190.50	$190.50
Purchase #7	$73.86	12.162%	$82.8429	$82.84	$82.85	$82.80
7 purchase totals =	$747.09		$820.7780	$820.77	$820.80	$820.80