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	$29.25	4.182%	$30.4732	$30.47	$30.45	$30.50
Purchase #2	$82.67	7.796%	$89.115	$89.12	$89.10	$89.10
Purchase #3	$247.74	11.243%	$275.5934	$275.59	$275.60	$275.60
Purchase #4	$13.83	10.115%	$15.2289	$15.23	$15.25	$15.20
Purchase #5	$26.54	12.592%	$29.8819	$29.88	$29.90	$29.90
Purchase #6	$150.34	9.318%	$164.3487	$164.35	$164.35	$164.30
Purchase #7	$16.51	11.707%	$18.4428	$18.44	$18.45	$18.40
7 purchase totals =	$566.88		$623.0839	$623.08	$623.10	$623.00