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	$5.47	10.772%	$6.0592	$6.06	$6.05	$6.10
Purchase #2	$146.43	6.139%	$155.4193	$155.42	$155.40	$155.40
Purchase #3	$9.25	12.180%	$10.3767	$10.38	$10.40	$10.40
Purchase #4	$123.88	13.726%	$140.8838	$140.88	$140.90	$140.90
Purchase #5	$38.91	10.362%	$42.9419	$42.94	$42.95	$42.90
Purchase #6	$133.65	13.248%	$151.356	$151.36	$151.35	$151.40
Purchase #7	$77.52	5.691%	$81.9317	$81.93	$81.95	$81.90
7 purchase totals =	$535.11		$588.9686	$588.97	$589.00	$589.00