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	$29.91	6.383%	$31.8192	$31.82	$31.80	$31.80
Purchase #2	$240.25	6.487%	$255.835	$255.84	$255.85	$255.80
Purchase #3	$49.35	11.220%	$54.8871	$54.89	$54.90	$54.90
Purchase #4	$167.72	10.693%	$185.6543	$185.65	$185.65	$185.70
Purchase #5	$199.51	10.496%	$220.4506	$220.45	$220.45	$220.50
Purchase #6	$39.26	13.138%	$44.418	$44.42	$44.40	$44.40
Purchase #7	$181.96	4.580%	$190.2938	$190.29	$190.30	$190.30
7 purchase totals =	$907.96		$983.3580	$983.36	$983.35	$983.40