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	$11.92	5.185%	$12.5381	$12.54	$12.55	$12.50
Purchase #2	$26.58	10.704%	$29.4251	$29.43	$29.45	$29.40
Purchase #3	$246.27	7.354%	$264.3807	$264.38	$264.40	$264.40
Purchase #4	$50.35	12.665%	$56.7268	$56.73	$56.75	$56.70
Purchase #5	$198.83	9.297%	$217.3152	$217.32	$217.30	$217.30
Purchase #6	$149.28	11.846%	$166.9637	$166.96	$166.95	$167.00
Purchase #7	$54.54	3.637%	$56.5236	$56.52	$56.50	$56.50
7 purchase totals =	$737.77		$803.8732	$803.88	$803.90	$803.80