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	$29.70	5.207%	$31.2465	$31.25	$31.25	$31.20
Purchase #2	$34.47	13.535%	$39.1355	$39.14	$39.15	$39.10
Purchase #3	$215.51	11.660%	$240.6385	$240.64	$240.65	$240.60
Purchase #4	$239.31	10.604%	$264.6864	$264.69	$264.70	$264.70
Purchase #5	$76.35	3.185%	$78.7817	$78.78	$78.80	$78.80
Purchase #6	$179.54	8.469%	$194.7452	$194.75	$194.75	$194.70
Purchase #7	$37.82	7.155%	$40.526	$40.53	$40.55	$40.50
7 purchase totals =	$812.70		$889.7598	$889.78	$889.85	$889.60