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	$37.96	12.659%	$42.7654	$42.77	$42.75	$42.80
Purchase #2	$95.83	7.236%	$102.7643	$102.76	$102.75	$102.80
Purchase #3	$172.92	13.665%	$196.5495	$196.55	$196.55	$196.50
Purchase #4	$144.31	5.327%	$151.9974	$152.00	$152.00	$152.00
Purchase #5	$237.51	12.529%	$267.2676	$267.27	$267.25	$267.30
Purchase #6	$105.39	5.550%	$111.2391	$111.24	$111.25	$111.20
Purchase #7	$82.68	8.119%	$89.3928	$89.39	$89.40	$89.40
7 purchase totals =	$876.60		$961.9761	$961.98	$961.95	$962.00