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	$240.58	7.822%	$259.3982	$259.40	$259.40	$259.40
Purchase #2	$157.56	7.103%	$168.7515	$168.75	$168.75	$168.80
Purchase #3	$48.41	13.733%	$55.0581	$55.06	$55.05	$55.10
Purchase #4	$244.50	4.670%	$255.9182	$255.92	$255.90	$255.90
Purchase #5	$52.65	10.766%	$58.3183	$58.32	$58.30	$58.30
Purchase #6	$127.48	10.244%	$140.5391	$140.54	$140.55	$140.50
Purchase #7	$59.96	13.356%	$67.9683	$67.97	$67.95	$68.00
7 purchase totals =	$931.14		$1,005.9517	$1,005.96	$1,005.90	$1,006.00