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	$99.95	11.669%	$111.6132	$111.61	$111.60	$111.60
Purchase #2	$66.97	4.478%	$69.9689	$69.97	$69.95	$70.00
Purchase #3	$120.63	8.770%	$131.2093	$131.21	$131.20	$131.20
Purchase #4	$62.83	7.440%	$67.5046	$67.50	$67.50	$67.50
Purchase #5	$136.83	12.419%	$153.8229	$153.82	$153.80	$153.80
Purchase #6	$250.56	11.386%	$279.0888	$279.09	$279.10	$279.10
Purchase #7	$178.51	5.438%	$188.2174	$188.22	$188.20	$188.20
7 purchase totals =	$916.28		$1,001.4251	$1,001.42	$1,001.35	$1,001.40