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	$17.59	5.445%	$18.5478	$18.55	$18.55	$18.50
Purchase #2	$24.81	12.300%	$27.8616	$27.86	$27.85	$27.90
Purchase #3	$46.74	11.617%	$52.1698	$52.17	$52.15	$52.20
Purchase #4	$59.95	3.517%	$62.0584	$62.06	$62.05	$62.10
Purchase #5	$100.92	4.457%	$105.418	$105.42	$105.40	$105.40
Purchase #6	$30.57	6.442%	$32.5393	$32.54	$32.55	$32.50
Purchase #7	$179.62	12.874%	$202.7443	$202.74	$202.75	$202.70
7 purchase totals =	$460.20		$501.3392	$501.34	$501.30	$501.30