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	$196.51	13.684%	$223.4004	$223.40	$223.40	$223.40
Purchase #2	$235.43	5.229%	$247.7406	$247.74	$247.75	$247.70
Purchase #3	$230.65	12.477%	$259.4282	$259.43	$259.45	$259.40
Purchase #4	$36.64	9.782%	$40.2241	$40.22	$40.20	$40.20
Purchase #5	$140.25	11.234%	$156.0057	$156.01	$156.00	$156.00
Purchase #6	$208.76	6.861%	$223.083	$223.08	$223.10	$223.10
Purchase #7	$138.25	7.675%	$148.8607	$148.86	$148.85	$148.90
7 purchase totals =	$1,186.49		$1,298.7427	$1,298.74	$1,298.75	$1,298.70