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	$213.41	5.837%	$225.8667	$225.87	$225.85	$225.90
Purchase #2	$92.86	12.647%	$104.604	$104.60	$104.60	$104.60
Purchase #3	$13.26	6.455%	$14.1159	$14.12	$14.10	$14.10
Purchase #4	$32.72	3.331%	$33.8099	$33.81	$33.80	$33.80
Purchase #5	$45.69	6.116%	$48.4844	$48.48	$48.50	$48.50
Purchase #6	$40.28	10.498%	$44.5086	$44.51	$44.50	$44.50
Purchase #7	$147.46	13.536%	$167.4202	$167.42	$167.40	$167.40
7 purchase totals =	$585.68		$638.8097	$638.81	$638.75	$638.80