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	$40.99	10.160%	$45.1546	$45.15	$45.15	$45.20
Purchase #2	$225.28	3.590%	$233.3676	$233.37	$233.35	$233.40
Purchase #3	$85.50	11.613%	$95.4291	$95.43	$95.45	$95.40
Purchase #4	$72.43	12.314%	$81.349	$81.35	$81.35	$81.30
Purchase #5	$71.91	12.450%	$80.8628	$80.86	$80.85	$80.90
Purchase #6	$24.88	4.278%	$25.9444	$25.94	$25.95	$25.90
Purchase #7	$44.44	12.639%	$50.0568	$50.06	$50.05	$50.10
7 purchase totals =	$565.43		$612.1643	$612.16	$612.15	$612.20