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	$68.45	5.226%	$72.0272	$72.03	$72.05	$72.00
Purchase #2	$89.69	4.375%	$93.6139	$93.61	$93.60	$93.60
Purchase #3	$81.90	8.734%	$89.0531	$89.05	$89.05	$89.10
Purchase #4	$231.58	12.241%	$259.9277	$259.93	$259.95	$259.90
Purchase #5	$159.57	10.691%	$176.6296	$176.63	$176.65	$176.60
Purchase #6	$158.68	4.435%	$165.7175	$165.72	$165.70	$165.70
Purchase #7	$149.38	4.722%	$156.4337	$156.43	$156.45	$156.40
7 purchase totals =	$939.25		$1,013.4027	$1,013.40	$1,013.45	$1,013.30