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	$51.69	9.608%	$56.6564	$56.66	$56.65	$56.70
Purchase #2	$205.57	3.293%	$212.3394	$212.34	$212.35	$212.30
Purchase #3	$90.45	11.167%	$100.5506	$100.55	$100.55	$100.60
Purchase #4	$73.88	11.802%	$82.5993	$82.60	$82.60	$82.60
Purchase #5	$218.32	9.678%	$239.449	$239.45	$239.45	$239.40
Purchase #6	$182.58	10.777%	$202.2566	$202.26	$202.25	$202.30
Purchase #7	$156.76	10.723%	$173.5694	$173.57	$173.55	$173.60
7 purchase totals =	$979.25		$1,067.4207	$1,067.43	$1,067.40	$1,067.50