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	$14.60	13.535%	$16.5761	$16.58	$16.60	$16.60
Purchase #2	$91.72	5.665%	$96.9159	$96.92	$96.90	$96.90
Purchase #3	$16.32	12.387%	$18.3416	$18.34	$18.35	$18.30
Purchase #4	$33.88	13.836%	$38.5676	$38.57	$38.55	$38.60
Purchase #5	$46.97	13.817%	$53.4598	$53.46	$53.45	$53.50
Purchase #6	$170.25	5.278%	$179.2358	$179.24	$179.25	$179.20
Purchase #7	$81.32	5.624%	$85.8934	$85.89	$85.90	$85.90
7 purchase totals =	$455.06		$488.9902	$489.00	$489.00	$489.00