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	$54.57	9.620%	$59.8196	$59.82	$59.80	$59.80
Purchase #2	$106.25	6.252%	$112.8928	$112.89	$112.90	$112.90
Purchase #3	$157.55	13.664%	$179.0776	$179.08	$179.10	$179.10
Purchase #4	$52.36	4.848%	$54.8984	$54.90	$54.90	$54.90
Purchase #5	$168.83	9.234%	$184.4198	$184.42	$184.40	$184.40
Purchase #6	$88.64	12.501%	$99.7209	$99.72	$99.70	$99.70
Purchase #7	$153.70	12.661%	$173.16	$173.16	$173.15	$173.20
7 purchase totals =	$781.90		$863.9891	$863.99	$863.95	$864.00