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	$5.63	8.788%	$6.1248	$6.12	$6.10	$6.10
Purchase #2	$59.81	13.602%	$67.9454	$67.95	$67.95	$67.90
Purchase #3	$41.51	10.582%	$45.9026	$45.90	$45.90	$45.90
Purchase #4	$16.41	13.345%	$18.5999	$18.60	$18.60	$18.60
Purchase #5	$217.88	5.849%	$230.6238	$230.62	$230.60	$230.60
Purchase #6	$101.46	7.750%	$109.3232	$109.32	$109.30	$109.30
Purchase #7	$209.48	12.136%	$234.9025	$234.90	$234.90	$234.90
7 purchase totals =	$652.18		$713.4222	$713.41	$713.35	$713.30