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	$36.28	8.869%	$39.4977	$39.50	$39.50	$39.50
Purchase #2	$144.49	6.623%	$154.0596	$154.06	$154.05	$154.10
Purchase #3	$97.56	6.676%	$104.0731	$104.07	$104.05	$104.10
Purchase #4	$119.86	8.601%	$130.1692	$130.17	$130.15	$130.20
Purchase #5	$224.47	9.512%	$245.8216	$245.82	$245.80	$245.80
Purchase #6	$80.81	10.149%	$89.0114	$89.01	$89.00	$89.00
Purchase #7	$131.91	13.762%	$150.0635	$150.06	$150.05	$150.10
7 purchase totals =	$835.38		$912.6961	$912.69	$912.60	$912.80