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	$19.68	3.665%	$20.4013	$20.40	$20.40	$20.40
Purchase #2	$133.83	12.744%	$150.8853	$150.89	$150.90	$150.90
Purchase #3	$137.94	8.812%	$150.0953	$150.10	$150.10	$150.10
Purchase #4	$114.70	12.102%	$128.581	$128.58	$128.60	$128.60
Purchase #5	$62.31	10.869%	$69.0825	$69.08	$69.10	$69.10
Purchase #6	$147.94	8.194%	$160.0622	$160.06	$160.05	$160.10
Purchase #7	$79.31	9.596%	$86.9206	$86.92	$86.90	$86.90
7 purchase totals =	$695.71		$766.0282	$766.03	$766.05	$766.10