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	$242.63	5.114%	$255.0381	$255.04	$255.05	$255.00
Purchase #2	$190.64	4.135%	$198.523	$198.52	$198.50	$198.50
Purchase #3	$47.27	7.125%	$50.638	$50.64	$50.65	$50.60
Purchase #4	$64.53	10.521%	$71.3192	$71.32	$71.30	$71.30
Purchase #5	$121.94	7.867%	$131.533	$131.53	$131.55	$131.50
Purchase #6	$183.30	13.167%	$207.4351	$207.44	$207.45	$207.40
Purchase #7	$231.43	4.542%	$241.9416	$241.94	$241.95	$241.90
7 purchase totals =	$1,081.74		$1,156.4280	$1,156.43	$1,156.45	$1,156.20