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	$241.86	9.318%	$264.3965	$264.40	$264.40	$264.40
Purchase #2	$52.53	6.347%	$55.8641	$55.86	$55.85	$55.90
Purchase #3	$136.63	6.688%	$145.7678	$145.77	$145.75	$145.80
Purchase #4	$245.89	11.487%	$274.1354	$274.14	$274.15	$274.10
Purchase #5	$105.98	6.405%	$112.768	$112.77	$112.75	$112.80
Purchase #6	$39.82	11.284%	$44.3133	$44.31	$44.30	$44.30
Purchase #7	$103.54	12.597%	$116.5829	$116.58	$116.60	$116.60
7 purchase totals =	$926.25		$1,013.8280	$1,013.83	$1,013.80	$1,013.90