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	$133.64	3.193%	$137.9071	$137.91	$137.90	$137.90
Purchase #2	$159.39	5.691%	$168.4609	$168.46	$168.45	$168.50
Purchase #3	$54.47	12.395%	$61.2216	$61.22	$61.20	$61.20
Purchase #4	$226.92	6.504%	$241.6789	$241.68	$241.70	$241.70
Purchase #5	$176.31	8.634%	$191.5326	$191.53	$191.55	$191.50
Purchase #6	$30.91	9.517%	$33.8517	$33.85	$33.85	$33.90
Purchase #7	$205.50	13.645%	$233.5405	$233.54	$233.55	$233.50
7 purchase totals =	$987.14		$1,068.1933	$1,068.19	$1,068.20	$1,068.20