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	$131.43	7.538%	$141.3372	$141.34	$141.35	$141.30
Purchase #2	$39.50	12.622%	$44.4857	$44.49	$44.50	$44.50
Purchase #3	$142.83	9.405%	$156.2632	$156.26	$156.25	$156.30
Purchase #4	$164.91	11.238%	$183.4426	$183.44	$183.45	$183.40
Purchase #5	$55.51	5.301%	$58.4526	$58.45	$58.45	$58.50
Purchase #6	$36.87	9.103%	$40.2263	$40.23	$40.25	$40.20
Purchase #7	$29.83	7.360%	$32.0255	$32.03	$32.05	$32.00
7 purchase totals =	$600.88		$656.2331	$656.24	$656.30	$656.20