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	$42.95	5.568%	$45.3415	$45.34	$45.35	$45.30
Purchase #2	$155.55	11.446%	$173.3543	$173.35	$173.35	$173.40
Purchase #3	$85.93	4.128%	$89.4772	$89.48	$89.50	$89.50
Purchase #4	$10.34	10.402%	$11.4156	$11.42	$11.40	$11.40
Purchase #5	$101.83	12.601%	$114.6616	$114.66	$114.65	$114.70
Purchase #6	$60.32	9.127%	$65.8254	$65.83	$65.85	$65.80
Purchase #7	$17.47	5.735%	$18.4719	$18.47	$18.45	$18.50
7 purchase totals =	$474.39		$518.5475	$518.55	$518.55	$518.60