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	$203.78	9.247%	$222.6235	$222.62	$222.60	$222.60
Purchase #2	$20.92	3.286%	$21.6074	$21.61	$21.60	$21.60
Purchase #3	$167.40	10.139%	$184.3727	$184.37	$184.35	$184.40
Purchase #4	$50.44	8.652%	$54.8041	$54.80	$54.80	$54.80
Purchase #5	$64.81	12.565%	$72.9534	$72.95	$72.95	$73.00
Purchase #6	$28.36	10.753%	$31.4096	$31.41	$31.40	$31.40
Purchase #7	$73.73	5.870%	$78.058	$78.06	$78.05	$78.10
7 purchase totals =	$609.44		$665.8287	$665.82	$665.75	$665.90