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	$114.92	3.753%	$119.2329	$119.23	$119.25	$119.20
Purchase #2	$155.53	3.166%	$160.4541	$160.45	$160.45	$160.50
Purchase #3	$29.90	4.209%	$31.1585	$31.16	$31.15	$31.20
Purchase #4	$50.70	11.229%	$56.3931	$56.39	$56.40	$56.40
Purchase #5	$66.44	4.260%	$69.2703	$69.27	$69.25	$69.30
Purchase #6	$50.40	3.523%	$52.1756	$52.18	$52.20	$52.20
Purchase #7	$28.88	12.746%	$32.561	$32.56	$32.55	$32.60
7 purchase totals =	$496.77		$521.2455	$521.24	$521.25	$521.40