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	$61.88	4.817%	$64.8608	$64.86	$64.85	$64.90
Purchase #2	$29.84	6.773%	$31.8611	$31.86	$31.85	$31.90
Purchase #3	$93.66	6.103%	$99.3761	$99.38	$99.40	$99.40
Purchase #4	$11.34	4.296%	$11.8272	$11.83	$11.85	$11.80
Purchase #5	$62.52	6.657%	$66.682	$66.68	$66.70	$66.70
Purchase #6	$82.78	4.533%	$86.5324	$86.53	$86.55	$86.50
Purchase #7	$186.25	12.613%	$209.7417	$209.74	$209.75	$209.70
7 purchase totals =	$528.27		$570.8813	$570.88	$570.95	$570.90