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	$19.59	4.799%	$20.5301	$20.53	$20.55	$20.50
Purchase #2	$112.81	13.143%	$127.6366	$127.64	$127.65	$127.60
Purchase #3	$190.29	4.755%	$199.3383	$199.34	$199.35	$199.30
Purchase #4	$124.47	10.427%	$137.4485	$137.45	$137.45	$137.40
Purchase #5	$246.55	5.378%	$259.8095	$259.81	$259.80	$259.80
Purchase #6	$24.42	3.821%	$25.3531	$25.35	$25.35	$25.40
Purchase #7	$14.35	6.690%	$15.31	$15.31	$15.30	$15.30
7 purchase totals =	$732.48		$785.4261	$785.43	$785.45	$785.30