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	$39.78	9.515%	$43.5651	$43.57	$43.55	$43.60
Purchase #2	$106.55	6.858%	$113.8572	$113.86	$113.85	$113.90
Purchase #3	$49.46	4.514%	$51.6926	$51.69	$51.70	$51.70
Purchase #4	$59.87	12.472%	$67.337	$67.34	$67.35	$67.30
Purchase #5	$55.40	10.359%	$61.1389	$61.14	$61.15	$61.10
Purchase #6	$124.92	10.573%	$138.1278	$138.13	$138.15	$138.10
Purchase #7	$24.82	10.828%	$27.5075	$27.51	$27.50	$27.50
7 purchase totals =	$460.80		$503.2261	$503.24	$503.25	$503.20