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	$231.38	7.327%	$248.3332	$248.33	$248.35	$248.30
Purchase #2	$19.44	3.265%	$20.0747	$20.07	$20.05	$20.10
Purchase #3	$143.39	13.413%	$162.6229	$162.62	$162.60	$162.60
Purchase #4	$180.75	5.828%	$191.2841	$191.28	$191.30	$191.30
Purchase #5	$176.55	11.516%	$196.8815	$196.88	$196.90	$196.90
Purchase #6	$117.28	11.462%	$130.7226	$130.72	$130.70	$130.70
Purchase #7	$44.39	9.698%	$48.6949	$48.69	$48.70	$48.70
7 purchase totals =	$913.18		$998.6139	$998.59	$998.60	$998.60